Module java.base
Package java.lang

Class String

java.lang.Object
java.lang.String
All Implemented Interfaces:
Serializable, CharSequence, Comparable<String>, Constable, ConstantDesc
public final class String extends Object implements Serializable, Comparable<String>, CharSequence, Constable, ConstantDesc
The String class represents character strings. All string literals in Java programs, such as "abc", are implemented as instances of this class.

Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared. For example: 

     String str = "abc";

is equivalent to: 

     char data[] = {'a', 'b', 'c'};
     String str = new String(data);

Here are some more examples of how strings can be used: 

     System.out.println("abc");
     String cde = "cde";
     System.out.println("abc" + cde);
     String c = "abc".substring(2, 3);
     String d = cde.substring(1, 2);

The class String includes methods for examining individual characters of the sequence, for comparing strings, for searching strings, for extracting substrings, and for creating a copy of a string with all characters translated to uppercase or to lowercase. Case mapping is based on the Unicode Standard version specified by the Character class.

The Java language provides special support for the string concatenation operator ( + ), and for conversion of other objects to strings. For additional information on string concatenation and conversion, see The Java Language Specification.

Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

A String represents a string in the UTF-16 format in which supplementary characters are represented by surrogate pairs (see the section Unicode Character Representations in the Character class for more information). Index values refer to char code units, so a supplementary character uses two positions in a String.

The String class provides methods for dealing with Unicode code points (i.e., characters), in addition to those for dealing with Unicode code units (i.e., char values).

Unless otherwise noted, methods for comparing Strings do not take locale into account. The Collator class provides methods for finer-grain, locale-sensitive String comparison.

Implementation Note:
The implementation of the string concatenation operator is left to the discretion of a Java compiler, as long as the compiler ultimately conforms to The Java Language Specification. For example, the javac compiler may implement the operator with StringBuffer, StringBuilder, or java.lang.invoke.StringConcatFactory depending on the JDK version. The implementation of string conversion is typically through the method toString, defined by Object and inherited by all classes in Java.
See Java Language Specification:
15.18.1 String Concatenation Operator +
Since:
1.0
See Also:

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final Comparator<String>
    CASE_INSENSITIVE_ORDER
    A Comparator that orders String objects as by compareToIgnoreCase.

  • Constructor Summary

    Constructors
    Constructor
    Description
    String()
    Initializes a newly created String object so that it represents an empty character sequence.
    String(byte[] bytes)
    Constructs a new String by decoding the specified array of bytes using the platform's default charset.
    String(byte[] ascii, int hibyte)
    Deprecated.
    This method does not properly convert bytes into characters.
    String(byte[] bytes, int offset, int length)
    Constructs a new String by decoding the specified subarray of bytes using the platform's default charset.
    String(byte[] ascii, int hibyte, int offset, int count)
    Deprecated.
    This method does not properly convert bytes into characters.
    String(byte[] bytes, int offset, int length, String charsetName)
    Constructs a new String by decoding the specified subarray of bytes using the specified charset.
    String(byte[] bytes, int offset, int length, Charset charset)
    Constructs a new String by decoding the specified subarray of bytes using the specified charset.
    String(byte[] bytes, String charsetName)
    Constructs a new String by decoding the specified array of bytes using the specified charset.
    String(byte[] bytes, Charset charset)
    Constructs a new String by decoding the specified array of bytes using the specified charset.
    String(char[] value)
    Allocates a new String so that it represents the sequence of characters currently contained in the character array argument.
    String(char[] value, int offset, int count)
    Allocates a new String that contains characters from a subarray of the character array argument.
    String(int[] codePoints, int offset, int count)
    Allocates a new String that contains characters from a subarray of the Unicode code point array argument.
    String(String original)
    Initializes a newly created String object so that it represents the same sequence of characters as the argument; in other words, the newly created string is a copy of the argument string.
    String(StringBuffer buffer)
    Allocates a new string that contains the sequence of characters currently contained in the string buffer argument.
    String(StringBuilder builder)
    Allocates a new string that contains the sequence of characters currently contained in the string builder argument.

  • Method Summary

    Modifier and Type
    Method
    Description
    char
    charAt(int index)
    Returns the char value at the specified index.
    IntStream
    chars()
    Returns a stream of int zero-extending the char values from this sequence.
    int
    codePointAt(int index)
    Returns the character (Unicode code point) at the specified index.
    int
    codePointBefore(int index)
    Returns the character (Unicode code point) before the specified index.
    int
    codePointCount(int beginIndex, int endIndex)
    Returns the number of Unicode code points in the specified text range of this String.
    IntStream
    codePoints()
    Returns a stream of code point values from this sequence.
    int
    compareTo(String anotherString)
    Compares two strings lexicographically.
    int
    compareToIgnoreCase(String str)
    Compares two strings lexicographically, ignoring case differences.
    String
    concat(String str)
    Concatenates the specified string to the end of this string.
    boolean
    contains(CharSequence s)
    Returns true if and only if this string contains the specified sequence of char values.
    boolean
    contentEquals(CharSequence cs)
    Compares this string to the specified CharSequence.
    boolean
    contentEquals(StringBuffer sb)
    Compares this string to the specified StringBuffer.
    static String
    copyValueOf(char[] data)
    Equivalent to valueOf(char[]).
    static String
    copyValueOf(char[] data, int offset, int count)
    Equivalent to valueOf(char[], int, int).
    Optional<String>
    describeConstable()
    Returns an Optional containing the nominal descriptor for this instance, which is the instance itself.
    boolean
    endsWith(String suffix)
    Tests if this string ends with the specified suffix.
    boolean
    equals(Object anObject)
    Compares this string to the specified object.
    boolean
    equalsIgnoreCase(String anotherString)
    Compares this String to another String, ignoring case considerations.
    static String
    format(String format, Object... args)
    Returns a formatted string using the specified format string and arguments.
    static String
    format(Locale l, String format, Object... args)
    Returns a formatted string using the specified locale, format string, and arguments.
    String
    formatted(Object... args)
    Formats using this string as the format string, and the supplied arguments.
    byte[]
    getBytes()
    Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
    void
    getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
    Deprecated.
    This method does not properly convert characters into bytes.
    byte[]
    getBytes(String charsetName)
    Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
    byte[]
    getBytes(Charset charset)
    Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.
    void
    getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
    Copies characters from this string into the destination character array.
    int
    hashCode()
    Returns a hash code for this string.
    String
    indent(int n)
    Adjusts the indentation of each line of this string based on the value of n, and normalizes line termination characters.
    int
    indexOf(int ch)
    Returns the index within this string of the first occurrence of the specified character.
    int
    indexOf(int ch, int fromIndex)
    Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
    int
    indexOf(String str)
    Returns the index within this string of the first occurrence of the specified substring.
    int
    indexOf(String str, int fromIndex)
    Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
    String
    intern()
    Returns a canonical representation for the string object.
    boolean
    isBlank()
    Returns true if the string is empty or contains only white space codepoints, otherwise false.
    boolean
    isEmpty()
    Returns true if, and only if, length() is 0.
    static String
    join(CharSequence delimiter, CharSequence... elements)
    Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter.
    static String
    join(CharSequence delimiter, Iterable<? extends CharSequence> elements)
    Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter.
    int
    lastIndexOf(int ch)
    Returns the index within this string of the last occurrence of the specified character.
    int
    lastIndexOf(int ch, int fromIndex)
    Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
    int
    lastIndexOf(String str)
    Returns the index within this string of the last occurrence of the specified substring.
    int
    lastIndexOf(String str, int fromIndex)
    Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
    int
    length()
    Returns the length of this string.
    Stream<String>
    lines()
    Returns a stream of lines extracted from this string, separated by line terminators.
    boolean
    matches(String regex)
    Tells whether or not this string matches the given regular expression.
    int
    offsetByCodePoints(int index, int codePointOffset)
    Returns the index within this String that is offset from the given index by codePointOffset code points.
    boolean
    regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
    Tests if two string regions are equal.
    boolean
    regionMatches(int toffset, String other, int ooffset, int len)
    Tests if two string regions are equal.
    String
    repeat(int count)
    Returns a string whose value is the concatenation of this string repeated count times.
    String
    replace(char oldChar, char newChar)
    Returns a string resulting from replacing all occurrences of oldChar in this string with newChar.
    String
    replace(CharSequence target, CharSequence replacement)
    Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
    String
    replaceAll(String regex, String replacement)
    Replaces each substring of this string that matches the given regular expression with the given replacement.
    String
    replaceFirst(String regex, String replacement)
    Replaces the first substring of this string that matches the given regular expression with the given replacement.
    String
    resolveConstantDesc(MethodHandles.Lookup lookup)
    Resolves this instance as a ConstantDesc, the result of which is the instance itself.
    String[]
    split(String regex)
    Splits this string around matches of the given regular expression.
    String[]
    split(String regex, int limit)
    Splits this string around matches of the given regular expression.
    boolean
    startsWith(String prefix)
    Tests if this string starts with the specified prefix.
    boolean
    startsWith(String prefix, int toffset)
    Tests if the substring of this string beginning at the specified index starts with the specified prefix.
    String
    strip()
    Returns a string whose value is this string, with all leading and trailing white space removed.
    String
    stripIndent()
    Returns a string whose value is this string, with incidental white space removed from the beginning and end of every line.
    String
    stripLeading()
    Returns a string whose value is this string, with all leading white space removed.
    String
    stripTrailing()
    Returns a string whose value is this string, with all trailing white space removed.
    CharSequence
    subSequence(int beginIndex, int endIndex)
    Returns a character sequence that is a subsequence of this sequence.
    String
    substring(int beginIndex)
    Returns a string that is a substring of this string.
    String
    substring(int beginIndex, int endIndex)
    Returns a string that is a substring of this string.
    char[]
    toCharArray()
    Converts this string to a new character array.
    String
    toLowerCase()
    Converts all of the characters in this String to lower case using the rules of the default locale.
    String
    toLowerCase(Locale locale)
    Converts all of the characters in this String to lower case using the rules of the given Locale.
    String
    toString()
    This object (which is already a string!)
    String
    toUpperCase()
    Converts all of the characters in this String to upper case using the rules of the default locale.
    String
    toUpperCase(Locale locale)
    Converts all of the characters in this String to upper case using the rules of the given Locale.
    <R> R
    transform(Function<? super String,? extends R> f)
    This method allows the application of a function to this string.
    String
    translateEscapes()
    Returns a string whose value is this string, with escape sequences translated as if in a string literal.
    String
    trim()
    Returns a string whose value is this string, with all leading and trailing space removed, where space is defined as any character whose codepoint is less than or equal to 'U+0020' (the space character).
    static String
    valueOf(boolean b)
    Returns the string representation of the boolean argument.
    static String
    valueOf(char c)
    Returns the string representation of the char argument.
    static String
    valueOf(char[] data)
    Returns the string representation of the char array argument.
    static String
    valueOf(char[] data, int offset, int count)
    Returns the string representation of a specific subarray of the char array argument.
    static String
    valueOf(double d)
    Returns the string representation of the double argument.
    static String
    valueOf(float f)
    Returns the string representation of the float argument.
    static String
    valueOf(int i)
    Returns the string representation of the int argument.
    static String
    valueOf(long l)
    Returns the string representation of the long argument.
    static String
    valueOf(Object obj)
    Returns the string representation of the Object argument.

    Methods declared in class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

  • Field Details

    • CASE_INSENSITIVE_ORDER

      public static final Comparator<String> CASE_INSENSITIVE_ORDER
      A Comparator that orders String objects as by compareToIgnoreCase. This comparator is serializable.

      Note that this Comparator does not take locale into account, and will result in an unsatisfactory ordering for certain locales. The Collator class provides locale-sensitive comparison.

      Since:
      1.2
      See Also:

  • Constructor Details

    • String

      public String()
      Initializes a newly created String object so that it represents an empty character sequence. Note that use of this constructor is unnecessary since Strings are immutable.

    • String

      public String(String original)
      Initializes a newly created String object so that it represents the same sequence of characters as the argument; in other words, the newly created string is a copy of the argument string. Unless an explicit copy of original is needed, use of this constructor is unnecessary since Strings are immutable.
      Parameters:
      original - A String

    • String

      public String(char[] value)
      Allocates a new String so that it represents the sequence of characters currently contained in the character array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the newly created string.
      Parameters:
      value - The initial value of the string

    • String

      public String(char[] value, int offset, int count)
      Allocates a new String that contains characters from a subarray of the character array argument. The offset argument is the index of the first character of the subarray and the count argument specifies the length of the subarray. The contents of the subarray are copied; subsequent modification of the character array does not affect the newly created string.
      Parameters:
      value - Array that is the source of characters
      offset - The initial offset
      count - The length
      Throws:
      IndexOutOfBoundsException - If offset is negative, count is negative, or offset is greater than value.length - count

    • String

      public String(int[] codePoints, int offset, int count)
      Allocates a new String that contains characters from a subarray of the Unicode code point array argument. The offset argument is the index of the first code point of the subarray and the count argument specifies the length of the subarray. The contents of the subarray are converted to chars; subsequent modification of the int array does not affect the newly created string.
      Parameters:
      codePoints - Array that is the source of Unicode code points
      offset - The initial offset
      count - The length
      Throws:
      IllegalArgumentException - If any invalid Unicode code point is found in codePoints
      IndexOutOfBoundsException - If offset is negative, count is negative, or offset is greater than codePoints.length - count
      Since:
      1.5

    • String

      @Deprecated(since="1.1") public String(byte[] ascii, int hibyte, int offset, int count)
      Deprecated.
      This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a Charset, charset name, or that use the platform's default charset.
      Allocates a new String constructed from a subarray of an array of 8-bit integer values.

      The offset argument is the index of the first byte of the subarray, and the count argument specifies the length of the subarray.

      Each byte in the subarray is converted to a char as specified in the String(byte[],int) constructor.

      Parameters:
      ascii - The bytes to be converted to characters
      hibyte - The top 8 bits of each 16-bit Unicode code unit
      offset - The initial offset
      count - The length
      Throws:
      IndexOutOfBoundsException - If offset is negative, count is negative, or offset is greater than ascii.length - count
      See Also:

    • String

      @Deprecated(since="1.1") public String(byte[] ascii, int hibyte)
      Deprecated.
      This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a Charset, charset name, or that use the platform's default charset.
      Allocates a new String containing characters constructed from an array of 8-bit integer values. Each character c in the resulting string is constructed from the corresponding component b in the byte array such that: 
           c == (char)(((hibyte & 0xff) << 8)
                         | (b & 0xff))
      Parameters:
      ascii - The bytes to be converted to characters
      hibyte - The top 8 bits of each 16-bit Unicode code unit
      See Also:

    • String

      public String(byte[] bytes, int offset, int length, String charsetName) throws UnsupportedEncodingException
      Constructs a new String by decoding the specified subarray of bytes using the specified charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the subarray.

      The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

      Parameters:
      bytes - The bytes to be decoded into characters
      offset - The index of the first byte to decode
      length - The number of bytes to decode
      charsetName - The name of a supported charset
      Throws:
      UnsupportedEncodingException - If the named charset is not supported
      IndexOutOfBoundsException - If offset is negative, length is negative, or offset is greater than bytes.length - length
      Since:
      1.1

    • String

      public String(byte[] bytes, int offset, int length, Charset charset)
      Constructs a new String by decoding the specified subarray of bytes using the specified charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the subarray.

      This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement string. The CharsetDecoder class should be used when more control over the decoding process is required.

      Parameters:
      bytes - The bytes to be decoded into characters
      offset - The index of the first byte to decode
      length - The number of bytes to decode
      charset - The charset to be used to decode the bytes
      Throws:
      IndexOutOfBoundsException - If offset is negative, length is negative, or offset is greater than bytes.length - length
      Since:
      1.6

    • String

      public String(byte[] bytes, String charsetName) throws UnsupportedEncodingException
      Constructs a new String by decoding the specified array of bytes using the specified charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the byte array.

      The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

      Parameters:
      bytes - The bytes to be decoded into characters
      charsetName - The name of a supported charset
      Throws:
      UnsupportedEncodingException - If the named charset is not supported
      Since:
      1.1

    • String

      public String(byte[] bytes, Charset charset)
      Constructs a new String by decoding the specified array of bytes using the specified charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the byte array.

      This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement string. The CharsetDecoder class should be used when more control over the decoding process is required.

      Parameters:
      bytes - The bytes to be decoded into characters
      charset - The charset to be used to decode the bytes
      Since:
      1.6

    • String

      public String(byte[] bytes, int offset, int length)
      Constructs a new String by decoding the specified subarray of bytes using the platform's default charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the subarray.

      The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

      Parameters:
      bytes - The bytes to be decoded into characters
      offset - The index of the first byte to decode
      length - The number of bytes to decode
      Throws:
      IndexOutOfBoundsException - If offset is negative, length is negative, or offset is greater than bytes.length - length
      Since:
      1.1

    • String

      public String(byte[] bytes)
      Constructs a new String by decoding the specified array of bytes using the platform's default charset. The length of the new String is a function of the charset, and hence may not be equal to the length of the byte array.

      The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.

      Parameters:
      bytes - The bytes to be decoded into characters
      Since:
      1.1

    • String

      public String(StringBuffer buffer)
      Allocates a new string that contains the sequence of characters currently contained in the string buffer argument. The contents of the string buffer are copied; subsequent modification of the string buffer does not affect the newly created string.
      Parameters:
      buffer - A StringBuffer

    • String

      public String(StringBuilder builder)
      Allocates a new string that contains the sequence of characters currently contained in the string builder argument. The contents of the string builder are copied; subsequent modification of the string builder does not affect the newly created string.

      This constructor is provided to ease migration to StringBuilder. Obtaining a string from a string builder via the toString method is likely to run faster and is generally preferred.

      Parameters:
      builder - A StringBuilder
      Since:
      1.5

  • Method Details

    • length

      public int length()
      Returns the length of this string. The length is equal to the number of Unicode code units in the string.
      Specified by:
      length in interface CharSequence
      Returns:
      the length of the sequence of characters represented by this object.

    • isEmpty

      public boolean isEmpty()
      Returns true if, and only if, length() is 0.
      Specified by:
      isEmpty in interface CharSequence
      Returns:
      true if length() is 0, otherwise false
      Since:
      1.6

    • charAt

      public char charAt(int index)
      Returns the char value at the specified index. An index ranges from 0 to length() - 1. The first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing.

      If the char value specified by the index is a surrogate, the surrogate value is returned.

      Specified by:
      charAt in interface CharSequence
      Parameters:
      index - the index of the char value.
      Returns:
      the char value at the specified index of this string. The first char value is at index 0.
      Throws:
      IndexOutOfBoundsException - if the index argument is negative or not less than the length of this string.

    • codePointAt

      public int codePointAt(int index)
      Returns the character (Unicode code point) at the specified index. The index refers to char values (Unicode code units) and ranges from 0 to length() - 1.

      If the char value specified at the given index is in the high-surrogate range, the following index is less than the length of this String, and the char value at the following index is in the low-surrogate range, then the supplementary code point corresponding to this surrogate pair is returned. Otherwise, the char value at the given index is returned.

      Parameters:
      index - the index to the char values
      Returns:
      the code point value of the character at the index
      Throws:
      IndexOutOfBoundsException - if the index argument is negative or not less than the length of this string.
      Since:
      1.5

    • codePointBefore

      public int codePointBefore(int index)
      Returns the character (Unicode code point) before the specified index. The index refers to char values (Unicode code units) and ranges from 1 to length.

      If the char value at (index - 1) is in the low-surrogate range, (index - 2) is not negative, and the char value at (index - 2) is in the high-surrogate range, then the supplementary code point value of the surrogate pair is returned. If the char value at index - 1 is an unpaired low-surrogate or a high-surrogate, the surrogate value is returned.

      Parameters:
      index - the index following the code point that should be returned
      Returns:
      the Unicode code point value before the given index.
      Throws:
      IndexOutOfBoundsException - if the index argument is less than 1 or greater than the length of this string.
      Since:
      1.5

    • codePointCount

      public int codePointCount(int beginIndex, int endIndex)
      Returns the number of Unicode code points in the specified text range of this String. The text range begins at the specified beginIndex and extends to the char at index endIndex - 1. Thus the length (in chars) of the text range is endIndex-beginIndex. Unpaired surrogates within the text range count as one code point each.
      Parameters:
      beginIndex - the index to the first char of the text range.
      endIndex - the index after the last char of the text range.
      Returns:
      the number of Unicode code points in the specified text range
      Throws:
      IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String, or beginIndex is larger than endIndex.
      Since:
      1.5

    • offsetByCodePoints

      public int offsetByCodePoints(int index, int codePointOffset)
      Returns the index within this String that is offset from the given index by codePointOffset code points. Unpaired surrogates within the text range given by index and codePointOffset count as one code point each.
      Parameters:
      index - the index to be offset
      codePointOffset - the offset in code points
      Returns:
      the index within this String
      Throws:
      IndexOutOfBoundsException - if index is negative or larger then the length of this String, or if codePointOffset is positive and the substring starting with index has fewer than codePointOffset code points, or if codePointOffset is negative and the substring before index has fewer than the absolute value of codePointOffset code points.
      Since:
      1.5

    • getChars

      public void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
      Copies characters from this string into the destination character array.

      The first character to be copied is at index srcBegin; the last character to be copied is at index srcEnd-1 (thus the total number of characters to be copied is srcEnd-srcBegin). The characters are copied into the subarray of dst starting at index dstBegin and ending at index: 

           dstBegin + (srcEnd-srcBegin) - 1
      Parameters:
      srcBegin - index of the first character in the string to copy.
      srcEnd - index after the last character in the string to copy.
      dst - the destination array.
      dstBegin - the start offset in the destination array.
      Throws:
      IndexOutOfBoundsException - If any of the following is true:
      • srcBegin is negative.
      • srcBegin is greater than srcEnd
      • srcEnd is greater than the length of this string
      • dstBegin is negative
      • dstBegin+(srcEnd-srcBegin) is larger than dst.length

    • getBytes

      @Deprecated(since="1.1") public void getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
      Deprecated.
      This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the getBytes() method, which uses the platform's default charset.
      Copies characters from this string into the destination byte array. Each byte receives the 8 low-order bits of the corresponding character. The eight high-order bits of each character are not copied and do not participate in the transfer in any way.

      The first character to be copied is at index srcBegin; the last character to be copied is at index srcEnd-1. The total number of characters to be copied is srcEnd-srcBegin. The characters, converted to bytes, are copied into the subarray of dst starting at index dstBegin and ending at index: 

           dstBegin + (srcEnd-srcBegin) - 1
      Parameters:
      srcBegin - Index of the first character in the string to copy
      srcEnd - Index after the last character in the string to copy
      dst - The destination array
      dstBegin - The start offset in the destination array
      Throws:
      IndexOutOfBoundsException - If any of the following is true:
      • srcBegin is negative
      • srcBegin is greater than srcEnd
      • srcEnd is greater than the length of this String
      • dstBegin is negative
      • dstBegin+(srcEnd-srcBegin) is larger than dst.length

    • getBytes

      public byte[] getBytes(String charsetName) throws UnsupportedEncodingException
      Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.

      The behavior of this method when this string cannot be encoded in the given charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.

      Parameters:
      charsetName - The name of a supported charset
      Returns:
      The resultant byte array
      Throws:
      UnsupportedEncodingException - If the named charset is not supported
      Since:
      1.1

    • getBytes

      public byte[] getBytes(Charset charset)
      Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.

      This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement byte array. The CharsetEncoder class should be used when more control over the encoding process is required.

      Parameters:
      charset - The Charset to be used to encode the String
      Returns:
      The resultant byte array
      Since:
      1.6

    • getBytes

      public byte[] getBytes()
      Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.

      The behavior of this method when this string cannot be encoded in the default charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.

      Returns:
      The resultant byte array
      Since:
      1.1

    • equals

      public boolean equals(Object anObject)
      Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.

      For finer-grained String comparison, refer to Collator.

      Overrides:
      equals in class Object
      Parameters:
      anObject - The object to compare this String against
      Returns:
      true if the given object represents a String equivalent to this string, false otherwise
      See Also:

    • contentEquals

      public boolean contentEquals(StringBuffer sb)
      Compares this string to the specified StringBuffer. The result is true if and only if this String represents the same sequence of characters as the specified StringBuffer. This method synchronizes on the StringBuffer.

      For finer-grained String comparison, refer to Collator.

      Parameters:
      sb - The StringBuffer to compare this String against
      Returns:
      true if this String represents the same sequence of characters as the specified StringBuffer, false otherwise
      Since:
      1.4

    • contentEquals

      public boolean contentEquals(CharSequence cs)
      Compares this string to the specified CharSequence. The result is true if and only if this String represents the same sequence of char values as the specified sequence. Note that if the CharSequence is a StringBuffer then the method synchronizes on it.

      For finer-grained String comparison, refer to Collator.

      Parameters:
      cs - The sequence to compare this String against
      Returns:
      true if this String represents the same sequence of char values as the specified sequence, false otherwise
      Since:
      1.5

    • equalsIgnoreCase

      public boolean equalsIgnoreCase(String anotherString)
      Compares this String to another String, ignoring case considerations. Two strings are considered equal ignoring case if they are of the same length and corresponding Unicode code points in the two strings are equal ignoring case.

      Two Unicode code points are considered the same ignoring case if at least one of the following is true:

      • The two Unicode code points are the same (as compared by the == operator)
      • Calling Character.toLowerCase(Character.toUpperCase(int)) on each Unicode code point produces the same result

      Note that this method does not take locale into account, and will result in unsatisfactory results for certain locales. The Collator class provides locale-sensitive comparison.

      Parameters:
      anotherString - The String to compare this String against
      Returns:
      true if the argument is not null and it represents an equivalent String ignoring case; false otherwise
      See Also:

    • compareTo

      public int compareTo(String anotherString)
      Compares two strings lexicographically. The comparison is based on the Unicode value of each character in the strings. The character sequence represented by this String object is compared lexicographically to the character sequence represented by the argument string. The result is a negative integer if this String object lexicographically precedes the argument string. The result is a positive integer if this String object lexicographically follows the argument string. The result is zero if the strings are equal; compareTo returns 0 exactly when the equals(Object) method would return true.

      This is the definition of lexicographic ordering. If two strings are different, then either they have different characters at some index that is a valid index for both strings, or their lengths are different, or both. If they have different characters at one or more index positions, let k be the smallest such index; then the string whose character at position k has the smaller value, as determined by using the < operator, lexicographically precedes the other string. In this case, compareTo returns the difference of the two character values at position k in the two string -- that is, the value: 

       this.charAt(k)-anotherString.charAt(k)
      If there is no index position at which they differ, then the shorter string lexicographically precedes the longer string. In this case, compareTo returns the difference of the lengths of the strings -- that is, the value: 
       this.length()-anotherString.length()

      For finer-grained String comparison, refer to Collator.

      Specified by:
      compareTo in interface Comparable<String>
      Parameters:
      anotherString - the String to be compared.
      Returns:
      the value 0 if the argument string is equal to this string; a value less than 0 if this string is lexicographically less than the string argument; and a value greater than 0 if this string is lexicographically greater than the string argument.

    • compareToIgnoreCase

      public int compareToIgnoreCase(String str)
      Compares two strings lexicographically, ignoring case differences. This method returns an integer whose sign is that of calling compareTo with case folded versions of the strings where case differences have been eliminated by calling Character.toLowerCase(Character.toUpperCase(int)) on each Unicode code point.

      Note that this method does not take locale into account, and will result in an unsatisfactory ordering for certain locales. The Collator class provides locale-sensitive comparison.

      Parameters:
      str - the String to be compared.
      Returns:
      a negative integer, zero, or a positive integer as the specified String is greater than, equal to, or less than this String, ignoring case considerations.
      Since:
      1.2
      See Also:

    • regionMatches

      public boolean regionMatches(int toffset, String other, int ooffset, int len)
      Tests if two string regions are equal.

      A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent identical character sequences. The substring of this String object to be compared begins at index toffset and has length len. The substring of other to be compared begins at index ooffset and has length len. The result is false if and only if at least one of the following is true:

      • toffset is negative.
      • ooffset is negative.
      • toffset+len is greater than the length of this String object.
      • ooffset+len is greater than the length of the other argument.
      • There is some nonnegative integer k less than len such that: this.charAt(toffset + k) != other.charAt(ooffset + k)

      Note that this method does not take locale into account. The Collator class provides locale-sensitive comparison.

      Parameters:
      toffset - the starting offset of the subregion in this string.
      other - the string argument.
      ooffset - the starting offset of the subregion in the string argument.
      len - the number of characters to compare.
      Returns:
      true if the specified subregion of this string exactly matches the specified subregion of the string argument; false otherwise.

    • regionMatches

      public boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
      Tests if two string regions are equal.

      A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent Unicode code point sequences that are the same, ignoring case if and only if ignoreCase is true. The sequences tsequence and osequence are compared, where tsequence is the sequence produced as if by calling this.substring(toffset, toffset + len).codePoints() and osequence is the sequence produced as if by calling other.substring(ooffset, ooffset + len).codePoints(). The result is true if and only if all of the following are true:

      • toffset is non-negative.
      • ooffset is non-negative.
      • toffset+len is less than or equal to the length of this String object.
      • ooffset+len is less than or equal to the length of the other argument.
      • if ignoreCase is false, all pairs of corresponding Unicode code points are equal integer values; or if ignoreCase is true, Character.toLowerCase( Character.toUpperCase(int)) on all pairs of Unicode code points results in equal integer values.

      Note that this method does not take locale into account, and will result in unsatisfactory results for certain locales when ignoreCase is true. The Collator class provides locale-sensitive comparison.

      Parameters:
      ignoreCase - if true, ignore case when comparing characters.
      toffset - the starting offset of the subregion in this string.
      other - the string argument.
      ooffset - the starting offset of the subregion in the string argument.
      len - the number of characters (Unicode code units - 16bit char value) to compare.
      Returns:
      true if the specified subregion of this string matches the specified subregion of the string argument; false otherwise. Whether the matching is exact or case insensitive depends on the ignoreCase argument.
      See Also:

    • startsWith

      public boolean startsWith(String prefix, int toffset)
      Tests if the substring of this string beginning at the specified index starts with the specified prefix.
      Parameters:
      prefix - the prefix.
      toffset - where to begin looking in this string.
      Returns:
      true if the character sequence represented by the argument is a prefix of the substring of this object starting at index toffset; false otherwise. The result is false if toffset is negative or greater than the length of this String object; otherwise the result is the same as the result of the expression 
                this.substring(toffset).startsWith(prefix)

    • startsWith

      public boolean startsWith(String prefix)
      Tests if this string starts with the specified prefix.
      Parameters:
      prefix - the prefix.
      Returns:
      true if the character sequence represented by the argument is a prefix of the character sequence represented by this string; false otherwise. Note also that true will be returned if the argument is an empty string or is equal to this String object as determined by the equals(Object) method.
      Since:
      1.0

    • endsWith

      public boolean endsWith(String suffix)
      Tests if this string ends with the specified suffix.
      Parameters:
      suffix - the suffix.
      Returns:
      true if the character sequence represented by the argument is a suffix of the character sequence represented by this object; false otherwise. Note that the result will be true if the argument is the empty string or is equal to this String object as determined by the equals(Object) method.

    • hashCode

      public int hashCode()
      Returns a hash code for this string. The hash code for a String object is computed as 
       s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
      using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero.)
      Overrides:
      hashCode in class Object
      Returns:
      a hash code value for this object.
      See Also:

    • indexOf

      public int indexOf(int ch)
      Returns the index within this string of the first occurrence of the specified character. If a character with value ch occurs in the character sequence represented by this String object, then the index (in Unicode code units) of the first such occurrence is returned. For values of ch in the range from 0 to 0xFFFF (inclusive), this is the smallest value k such that: 
       this.charAt(k) == ch
      is true. For other values of ch, it is the smallest value k such that: 
       this.codePointAt(k) == ch
      is true. In either case, if no such character occurs in this string, then -1 is returned.
      Parameters:
      ch - a character (Unicode code point).
      Returns:
      the index of the first occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

    • indexOf

      public int indexOf(int ch, int fromIndex)
      Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.

      If a character with value ch occurs in the character sequence represented by this String object at an index no smaller than fromIndex, then the index of the first such occurrence is returned. For values of ch in the range from 0 to 0xFFFF (inclusive), this is the smallest value k such that: 

       (this.charAt(k) == ch) && (k >= fromIndex)
      is true. For other values of ch, it is the smallest value k such that: 
       (this.codePointAt(k) == ch) && (k >= fromIndex)
      is true. In either case, if no such character occurs in this string at or after position fromIndex, then -1 is returned.

      There is no restriction on the value of fromIndex. If it is negative, it has the same effect as if it were zero: this entire string may be searched. If it is greater than the length of this string, it has the same effect as if it were equal to the length of this string: -1 is returned.

      All indices are specified in char values (Unicode code units).

      Parameters:
      ch - a character (Unicode code point).
      fromIndex - the index to start the search from.
      Returns:
      the index of the first occurrence of the character in the character sequence represented by this object that is greater than or equal to fromIndex, or -1 if the character does not occur.

    • lastIndexOf

      public int lastIndexOf(int ch)
      Returns the index within this string of the last occurrence of the specified character. For values of ch in the range from 0 to 0xFFFF (inclusive), the index (in Unicode code units) returned is the largest value k such that: 
       this.charAt(k) == ch
      is true. For other values of ch, it is the largest value k such that: 
       this.codePointAt(k) == ch
      is true. In either case, if no such character occurs in this string, then -1 is returned. The String is searched backwards starting at the last character.
      Parameters:
      ch - a character (Unicode code point).
      Returns:
      the index of the last occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

    • lastIndexOf

      public int lastIndexOf(int ch, int fromIndex)
      Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index. For values of ch in the range from 0 to 0xFFFF (inclusive), the index returned is the largest value k such that: 
       (this.charAt(k) == ch) && (k <= fromIndex)
      is true. For other values of ch, it is the largest value k such that: 
       (this.codePointAt(k) == ch) && (k <= fromIndex)
      is true. In either case, if no such character occurs in this string at or before position fromIndex, then -1 is returned.

      All indices are specified in char values (Unicode code units).

      Parameters:
      ch - a character (Unicode code point).
      fromIndex - the index to start the search from. There is no restriction on the value of fromIndex. If it is greater than or equal to the length of this string, it has the same effect as if it were equal to one less than the length of this string: this entire string may be searched. If it is negative, it has the same effect as if it were -1: -1 is returned.
      Returns:
      the index of the last occurrence of the character in the character sequence represented by this object that is less than or equal to fromIndex, or -1 if the character does not occur before that point.

    • indexOf

      public int indexOf(String str)
      Returns the index within this string of the first occurrence of the specified substring.

      The returned index is the smallest value k for which: 

      
 this.startsWith(str, k)
      If no such value of k exists, then -1 is returned.
      Parameters:
      str - the substring to search for.
      Returns:
      the index of the first occurrence of the specified substring, or -1 if there is no such occurrence.

    • indexOf

      public int indexOf(String str, int fromIndex)
      Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.

      The returned index is the smallest value k for which: 

      
     k >= Math.min(fromIndex, this.length()) &&
                   this.startsWith(str, k)
      If no such value of k exists, then -1 is returned.
      Parameters:
      str - the substring to search for.
      fromIndex - the index from which to start the search.
      Returns:
      the index of the first occurrence of the specified substring, starting at the specified index, or -1 if there is no such occurrence.

    • lastIndexOf

      public int lastIndexOf(String str)
      Returns the index within this string of the last occurrence of the specified substring. The last occurrence of the empty string "" is considered to occur at the index value this.length().

      The returned index is the largest value k for which: 

      
 this.startsWith(str, k)
      If no such value of k exists, then -1 is returned.
      Parameters:
      str - the substring to search for.
      Returns:
      the index of the last occurrence of the specified substring, or -1 if there is no such occurrence.

    • lastIndexOf

      public int lastIndexOf(String str, int fromIndex)
      Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.

      The returned index is the largest value k for which: 

      
     k <= Math.min(fromIndex, this.length()) &&
                   this.startsWith(str, k)
      If no such value of k exists, then -1 is returned.
      Parameters:
      str - the substring to search for.
      fromIndex - the index to start the search from.
      Returns:
      the index of the last occurrence of the specified substring, searching backward from the specified index, or -1 if there is no such occurrence.

    • substring

      public String substring(int beginIndex)
      Returns a string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.

      Examples: 

       "unhappy".substring(2) returns "happy"
 "Harbison".substring(3) returns "bison"
 "emptiness".substring(9) returns "" (an empty string)
      Parameters:
      beginIndex - the beginning index, inclusive.
      Returns:
      the specified substring.
      Throws:
      IndexOutOfBoundsException - if beginIndex is negative or larger than the length of this String object.

    • substring

      public String substring(int beginIndex, int endIndex)
      Returns a string that is a substring of this string. The substring begins at the specified beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring is endIndex-beginIndex.

      Examples: 

       "hamburger".substring(4, 8) returns "urge"
 "smiles".substring(1, 5) returns "mile"
      Parameters:
      beginIndex - the beginning index, inclusive.
      endIndex - the ending index, exclusive.
      Returns:
      the specified substring.
      Throws:
      IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

    • subSequence

      public CharSequence subSequence(int beginIndex, int endIndex)
      Returns a character sequence that is a subsequence of this sequence.

      An invocation of this method of the form 

       str.subSequence(begin, end)
      behaves in exactly the same way as the invocation 
       str.substring(begin, end)
      Specified by:
      subSequence in interface CharSequence
      API Note:
      This method is defined so that the String class can implement the CharSequence interface.
      Parameters:
      beginIndex - the begin index, inclusive.
      endIndex - the end index, exclusive.
      Returns:
      the specified subsequence.
      Throws:
      IndexOutOfBoundsException - if beginIndex or endIndex is negative, if endIndex is greater than length(), or if beginIndex is greater than endIndex
      Since:
      1.4

    • concat

      public String concat(String str)
      Concatenates the specified string to the end of this string.

      If the length of the argument string is 0, then this String object is returned. Otherwise, a String object is returned that represents a character sequence that is the concatenation of the character sequence represented by this String object and the character sequence represented by the argument string.

      Examples: 

       "cares".concat("s") returns "caress"
 "to".concat("get").concat("her") returns "together"
      Parameters:
      str - the String that is concatenated to the end of this String.
      Returns:
      a string that represents the concatenation of this object's characters followed by the string argument's characters.

    • replace

      public String replace(char oldChar, char newChar)
      Returns a string resulting from replacing all occurrences of oldChar in this string with newChar.

      If the character oldChar does not occur in the character sequence represented by this String object, then a reference to this String object is returned. Otherwise, a String object is returned that represents a character sequence identical to the character sequence represented by this String object, except that every occurrence of oldChar is replaced by an occurrence of newChar.

      Examples: 

       "mesquite in your cellar".replace('e', 'o')
         returns "mosquito in your collar"
 "the war of baronets".replace('r', 'y')
         returns "the way of bayonets"
 "sparring with a purple porpoise".replace('p', 't')
         returns "starring with a turtle tortoise"
 "JonL".replace('q', 'x') returns "JonL" (no change)
      Parameters:
      oldChar - the old character.
      newChar - the new character.
      Returns:
      a string derived from this string by replacing every occurrence of oldChar with newChar.

    • matches

      public boolean matches(String regex)
      Tells whether or not this string matches the given regular expression.

      An invocation of this method of the form str.matches(regex) yields exactly the same result as the expression

      Pattern.matches(regex, str)
      Parameters:
      regex - the regular expression to which this string is to be matched
      Returns:
      true if, and only if, this string matches the given regular expression
      Throws:
      PatternSyntaxException - if the regular expression's syntax is invalid
      Since:
      1.4
      See Also:

    • contains

      public boolean contains(CharSequence s)
      Returns true if and only if this string contains the specified sequence of char values.
      Parameters:
      s - the sequence to search for
      Returns:
      true if this string contains s, false otherwise
      Since:
      1.5

    • replaceFirst

      public String replaceFirst(String regex, String replacement)
      Replaces the first substring of this string that matches the given regular expression with the given replacement.

      An invocation of this method of the form str.replaceFirst(regex, repl) yields exactly the same result as the expression

      Pattern.compile(regex).matcher(str).replaceFirst(repl)

      Note that backslashes (\) and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string; see Matcher.replaceFirst(java.lang.String). Use Matcher.quoteReplacement(java.lang.String) to suppress the special meaning of these characters, if desired.

      Parameters:
      regex - the regular expression to which this string is to be matched
      replacement - the string to be substituted for the first match
      Returns:
      The resulting String
      Throws:
      PatternSyntaxException - if the regular expression's syntax is invalid
      Since:
      1.4
      See Also:

    • replaceAll

      public String replaceAll(String regex, String replacement)
      Replaces each substring of this string that matches the given regular expression with the given replacement.

      An invocation of this method of the form str.replaceAll(regex, repl) yields exactly the same result as the expression

      Pattern.compile(regex).matcher(str).replaceAll(repl)

      Note that backslashes (\) and dollar signs ($) in the replacement string may cause the results to be different than if it were being treated as a literal replacement string; see Matcher.replaceAll. Use Matcher.quoteReplacement(java.lang.String) to suppress the special meaning of these characters, if desired.

      Parameters:
      regex - the regular expression to which this string is to be matched
      replacement - the string to be substituted for each match
      Returns:
      The resulting String
      Throws:
      PatternSyntaxException - if the regular expression's syntax is invalid
      Since:
      1.4
      See Also:

    • replace

      public String replace(CharSequence target, CharSequence replacement)
      Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence. The replacement proceeds from the beginning of the string to the end, for example, replacing "aa" with "b" in the string "aaa" will result in "ba" rather than "ab".
      Parameters:
      target - The sequence of char values to be replaced
      replacement - The replacement sequence of char values
      Returns:
      The resulting string
      Since:
      1.5

    • split

      public String[] split(String regex, int limit)
      Splits this string around matches of the given regular expression.

      The array returned by this method contains each substring of this string that is terminated by another substring that matches the given expression or is terminated by the end of the string. The substrings in the array are in the order in which they occur in this string. If the expression does not match any part of the input then the resulting array has just one element, namely this string.

      When there is a positive-width match at the beginning of this string then an empty leading substring is included at the beginning of the resulting array. A zero-width match at the beginning however never produces such empty leading substring.

      The limit parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array.

      • If the limit is positive then the pattern will be applied at most limit - 1 times, the array's length will be no greater than limit, and the array's last entry will contain all input beyond the last matched delimiter.

      • If the limit is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.

      • If the limit is negative then the pattern will be applied as many times as possible and the array can have any length.

      The string "boo:and:foo", for example, yields the following results with these parameters:

      Split example showing regex, limit, and result
      Regex Limit Result
      : 2 { "boo", "and:foo" }
      5 { "boo", "and", "foo" }
      -2 { "boo", "and", "foo" }
      o 5 { "b", "", ":and:f", "", "" }
      -2 { "b", "", ":and:f", "", "" }
      0 { "b", "", ":and:f" }

      An invocation of this method of the form str.split(regex, n) yields the same result as the expression

      Pattern.compile(regex).split(str, n)
      Parameters:
      regex - the delimiting regular expression
      limit - the result threshold, as described above
      Returns:
      the array of strings computed by splitting this string around matches of the given regular expression
      Throws:
      PatternSyntaxException - if the regular expression's syntax is invalid
      Since:
      1.4
      See Also:

    • split

      public String[] split(String regex)
      Splits this string around matches of the given regular expression.

      This method works as if by invoking the two-argument split method with the given expression and a limit argument of zero. Trailing empty strings are therefore not included in the resulting array.

      The string "boo:and:foo", for example, yields the following results with these expressions:

      Split examples showing regex and result
      Regex Result
      : { "boo", "and", "foo" }
      o { "b", "", ":and:f" }
      Parameters:
      regex - the delimiting regular expression
      Returns:
      the array of strings computed by splitting this string around matches of the given regular expression
      Throws:
      PatternSyntaxException - if the regular expression's syntax is invalid
      Since:
      1.4
      See Also:

    • join

      public static String join(CharSequence delimiter, CharSequence... elements)
      Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter.
      For example, 
      
     String message = String.join("-", "Java", "is", "cool");
     // message returned is: "Java-is-cool"
      Note that if an element is null, then "null" is added.
      Parameters:
      delimiter - the delimiter that separates each element
      elements - the elements to join together.
      Returns:
      a new String that is composed of the elements separated by the delimiter
      Throws:
      NullPointerException - If delimiter or elements is null
      Since:
      1.8
      See Also:

    • join

      public static String join(CharSequence delimiter, Iterable<? extends CharSequence> elements)
      Returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter.
      For example, 
      
     List<String> strings = List.of("Java", "is", "cool");
     String message = String.join(" ", strings);
     // message returned is: "Java is cool"

     Set<String> strings =
         new LinkedHashSet<>(List.of("Java", "is", "very", "cool"));
     String message = String.join("-", strings);
     // message returned is: "Java-is-very-cool"
      Note that if an individual element is null, then "null" is added.
      Parameters:
      delimiter - a sequence of characters that is used to separate each of the elements in the resulting String
      elements - an Iterable that will have its elements joined together.
      Returns:
      a new String that is composed from the elements argument
      Throws:
      NullPointerException - If delimiter or elements is null
      Since:
      1.8
      See Also:

    • toLowerCase

      public String toLowerCase(Locale locale)
      Converts all of the characters in this String to lower case using the rules of the given Locale. Case mapping is based on the Unicode Standard version specified by the Character class. Since case mappings are not always 1:1 char mappings, the resulting String may be a different length than the original String.

      Examples of lowercase mappings are in the following table:

      Lowercase mapping examples showing language code of locale, upper case, lower case, and description
      Language Code of Locale Upper Case Lower Case Description
      tr (Turkish) \u0130 \u0069 capital letter I with dot above -> small letter i
      tr (Turkish) \u0049 \u0131 capital letter I -> small letter dotless i
      (all) French Fries french fries lowercased all chars in String
      (all) ΙΧΘΥΣ ιχθυσ lowercased all chars in String
      Parameters:
      locale - use the case transformation rules for this locale
      Returns:
      the String, converted to lowercase.
      Since:
      1.1
      See Also:

    • toLowerCase

      public String toLowerCase()
      Converts all of the characters in this String to lower case using the rules of the default locale. This is equivalent to calling toLowerCase(Locale.getDefault()).

      Note: This method is locale sensitive, and may produce unexpected results if used for strings that are intended to be interpreted locale independently. Examples are programming language identifiers, protocol keys, and HTML tags. For instance, "TITLE".toLowerCase() in a Turkish locale returns "t\u0131tle", where '\u0131' is the LATIN SMALL LETTER DOTLESS I character. To obtain correct results for locale insensitive strings, use toLowerCase(Locale.ROOT).

      Returns:
      the String, converted to lowercase.
      See Also:

    • toUpperCase

      public String toUpperCase(Locale locale)
      Converts all of the characters in this String to upper case using the rules of the given Locale. Case mapping is based on the Unicode Standard version specified by the Character class. Since case mappings are not always 1:1 char mappings, the resulting String may be a different length than the original String.

      Examples of locale-sensitive and 1:M case mappings are in the following table.

      Examples of locale-sensitive and 1:M case mappings. Shows Language code of locale, lower case, upper case, and description.
      Language Code of Locale Lower Case Upper Case Description
      tr (Turkish) \u0069 \u0130 small letter i -> capital letter I with dot above
      tr (Turkish) \u0131 \u0049 small letter dotless i -> capital letter I
      (all) \u00df \u0053 \u0053 small letter sharp s -> two letters: SS
      (all) Fahrvergnügen FAHRVERGNÜGEN
      Parameters:
      locale - use the case transformation rules for this locale
      Returns:
      the String, converted to uppercase.
      Since:
      1.1
      See Also:

    • toUpperCase

      public String toUpperCase()
      Converts all of the characters in this String to upper case using the rules of the default locale. This method is equivalent to toUpperCase(Locale.getDefault()).

      Note: This method is locale sensitive, and may produce unexpected results if used for strings that are intended to be interpreted locale independently. Examples are programming language identifiers, protocol keys, and HTML tags. For instance, "title".toUpperCase() in a Turkish locale returns "T\u0130TLE", where '\u0130' is the LATIN CAPITAL LETTER I WITH DOT ABOVE character. To obtain correct results for locale insensitive strings, use toUpperCase(Locale.ROOT).

      Returns:
      the String, converted to uppercase.
      See Also:

    • trim

      public String trim()
      Returns a string whose value is this string, with all leading and trailing space removed, where space is defined as any character whose codepoint is less than or equal to 'U+0020' (the space character).

      If this String object represents an empty character sequence, or the first and last characters of character sequence represented by this String object both have codes that are not space (as defined above), then a reference to this String object is returned.

      Otherwise, if all characters in this string are space (as defined above), then a String object representing an empty string is returned.

      Otherwise, let k be the index of the first character in the string whose code is not a space (as defined above) and let m be the index of the last character in the string whose code is not a space (as defined above). A String object is returned, representing the substring of this string that begins with the character at index k and ends with the character at index m-that is, the result of this.substring(k, m + 1).

      This method may be used to trim space (as defined above) from the beginning and end of a string.

      Returns:
      a string whose value is this string, with all leading and trailing space removed, or this string if it has no leading or trailing space.

    • strip

      public String strip()
      Returns a string whose value is this string, with all leading and trailing white space removed.

      If this String object represents an empty string, or if all code points in this string are white space, then an empty string is returned.

      Otherwise, returns a substring of this string beginning with the first code point that is not a white space up to and including the last code point that is not a white space.

      This method may be used to strip white space from the beginning and end of a string.

      Returns:
      a string whose value is this string, with all leading and trailing white space removed
      Since:
      11
      See Also:

    • stripLeading

      public String stripLeading()
      Returns a string whose value is this string, with all leading white space removed.

      If this String object represents an empty string, or if all code points in this string are white space, then an empty string is returned.

      Otherwise, returns a substring of this string beginning with the first code point that is not a white space up to and including the last code point of this string.

      This method may be used to trim white space from the beginning of a string.

      Returns:
      a string whose value is this string, with all leading white space removed
      Since:
      11
      See Also:

    • stripTrailing

      public String stripTrailing()
      Returns a string whose value is this string, with all trailing white space removed.

      If this String object represents an empty string, or if all characters in this string are white space, then an empty string is returned.

      Otherwise, returns a substring of this string beginning with the first code point of this string up to and including the last code point that is not a white space.

      This method may be used to trim white space from the end of a string.

      Returns:
      a string whose value is this string, with all trailing white space removed
      Since:
      11
      See Also:

    • isBlank

      public boolean isBlank()
      Returns true if the string is empty or contains only white space codepoints, otherwise false.
      Returns:
      true if the string is empty or contains only white space codepoints, otherwise false
      Since:
      11
      See Also:

    • lines

      public Stream<String> lines()
      Returns a stream of lines extracted from this string, separated by line terminators.

      A line terminator is one of the following: a line feed character "\n" (U+000A), a carriage return character "\r" (U+000D), or a carriage return followed immediately by a line feed "\r\n" (U+000D U+000A).

      A line is either a sequence of zero or more characters followed by a line terminator, or it is a sequence of one or more characters followed by the end of the string. A line does not include the line terminator.

      The stream returned by this method contains the lines from this string in the order in which they occur.

      API Note:
      This definition of line implies that an empty string has zero lines and that there is no empty line following a line terminator at the end of a string.
      Implementation Note:
      This method provides better performance than split("\R") by supplying elements lazily and by faster search of new line terminators.
      Returns:
      the stream of lines extracted from this string
      Since:
      11

    • indent

      public String indent(int n)
      Adjusts the indentation of each line of this string based on the value of n, and normalizes line termination characters.

      This string is conceptually separated into lines using lines(). Each line is then adjusted as described below and then suffixed with a line feed "\n" (U+000A). The resulting lines are then concatenated and returned.

      If n > 0 then n spaces (U+0020) are inserted at the beginning of each line.

      If n < 0 then up to n white space characters are removed from the beginning of each line. If a given line does not contain sufficient white space then all leading white space characters are removed. Each white space character is treated as a single character. In particular, the tab character "\t" (U+0009) is considered a single character; it is not expanded.

      If n == 0 then the line remains unchanged. However, line terminators are still normalized.

      Parameters:
      n - number of leading white space characters to add or remove
      Returns:
      string with indentation adjusted and line endings normalized
      Since:
      12
      See Also:

    • stripIndent

      public String stripIndent()
      Returns a string whose value is this string, with incidental white space removed from the beginning and end of every line.

      Incidental white space is often present in a text block to align the content with the opening delimiter. For example, in the following code, dots represent incidental white space: 

       String html = """
 ..............<html>
 ..............    <body>
 ..............        <p>Hello, world</p>
 ..............    </body>
 ..............</html>
 ..............""";
      This method treats the incidental white space as indentation to be stripped, producing a string that preserves the relative indentation of the content. Using | to visualize the start of each line of the string: 
       |<html>
 |    <body>
 |        <p>Hello, world</p>
 |    </body>
 |</html>
      First, the individual lines of this string are extracted. A line is a sequence of zero or more characters followed by either a line terminator or the end of the string. If the string has at least one line terminator, the last line consists of the characters between the last terminator and the end of the string. Otherwise, if the string has no terminators, the last line is the start of the string to the end of the string, in other words, the entire string. A line does not include the line terminator.

      Then, the minimum indentation (min) is determined as follows:

      • For each non-blank line (as defined by isBlank()), the leading white space characters are counted.

      • The leading white space characters on the last line are also counted even if blank.

      The min value is the smallest of these counts.

      For each non-blank line, min leading white space characters are removed, and any trailing white space characters are removed. Blank lines are replaced with the empty string.

      Finally, the lines are joined into a new string, using the LF character "\n" (U+000A) to separate lines.

      API Note:
      This method's primary purpose is to shift a block of lines as far as possible to the left, while preserving relative indentation. Lines that were indented the least will thus have no leading white space. The result will have the same number of line terminators as this string. If this string ends with a line terminator then the result will end with a line terminator.
      Implementation Requirements:
      This method treats all white space characters as having equal width. As long as the indentation on every line is consistently composed of the same character sequences, then the result will be as described above.
      Returns:
      string with incidental indentation removed and line terminators normalized
      Since:
      15
      See Also:

    • translateEscapes

      public String translateEscapes()
      Returns a string whose value is this string, with escape sequences translated as if in a string literal.

      Escape sequences are translated as follows;

      Translation
      Escape Name Translation
      \b backspace U+0008
      \t horizontal tab U+0009
      \n line feed U+000A
      \f form feed U+000C
      \r carriage return U+000D
      \s space U+0020
      \" double quote U+0022
      \' single quote U+0027
      \\ backslash U+005C
      \0 - \377 octal escape code point equivalents
      \<line-terminator> continuation discard
      Implementation Note:
      This method does not translate Unicode escapes such as "\u2022". Unicode escapes are translated by the Java compiler when reading input characters and are not part of the string literal specification.
      Returns:
      String with escape sequences translated.
      Throws:
      IllegalArgumentException - when an escape sequence is malformed.
      See Java Language Specification:
      3.10.7 Escape Sequences
      Since:
      15

    • transform

      public <R> R transform(Function<? super String,? extends R> f)
      This method allows the application of a function to this string. The function should expect a single String argument and produce an R result.

      Any exception thrown by f.apply() will be propagated to the caller.

      Type Parameters:
      R - the type of the result
      Parameters:
      f - a function to apply
      Returns:
      the result of applying the function to this string
      Since:
      12
      See Also:

    • toString

      public String toString()
      This object (which is already a string!) is itself returned.
      Specified by:
      toString in interface CharSequence
      Overrides:
      toString in class Object
      Returns:
      the string itself.

    • chars

      public IntStream chars()
      Returns a stream of int zero-extending the char values from this sequence. Any char which maps to a surrogate code point is passed through uninterpreted.
      Specified by:
      chars in interface CharSequence
      Returns:
      an IntStream of char values from this sequence
      Since:
      9

    • codePoints

      public IntStream codePoints()
      Returns a stream of code point values from this sequence. Any surrogate pairs encountered in the sequence are combined as if by Character.toCodePoint and the result is passed to the stream. Any other code units, including ordinary BMP characters, unpaired surrogates, and undefined code units, are zero-extended to int values which are then passed to the stream.
      Specified by:
      codePoints in interface CharSequence
      Returns:
      an IntStream of Unicode code points from this sequence
      Since:
      9

    • toCharArray

      public char[] toCharArray()
      Converts this string to a new character array.
      Returns:
      a newly allocated character array whose length is the length of this string and whose contents are initialized to contain the character sequence represented by this string.

    • format

      public static String format(String format, Object... args)
      Returns a formatted string using the specified format string and arguments.

      The locale always used is the one returned by Locale.getDefault(Locale.Category) with FORMAT category specified.

      Parameters:
      format - A format string
      args - Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The number of arguments is variable and may be zero. The maximum number of arguments is limited by the maximum dimension of a Java array as defined by The Java Virtual Machine Specification. The behaviour on a null argument depends on the conversion.
      Returns:
      A formatted string
      Throws:
      IllegalFormatException - If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification.
      Since:
      1.5
      See Also:

    • format

      public static String format(Locale l, String format, Object... args)
      Returns a formatted string using the specified locale, format string, and arguments.
      Parameters:
      l - The locale to apply during formatting. If l is null then no localization is applied.
      format - A format string
      args - Arguments referenced by the format specifiers in the format string. If there are more arguments than format specifiers, the extra arguments are ignored. The number of arguments is variable and may be zero. The maximum number of arguments is limited by the maximum dimension of a Java array as defined by The Java Virtual Machine Specification. The behaviour on a null argument depends on the conversion.
      Returns:
      A formatted string
      Throws:
      IllegalFormatException - If a format string contains an illegal syntax, a format specifier that is incompatible with the given arguments, insufficient arguments given the format string, or other illegal conditions. For specification of all possible formatting errors, see the Details section of the formatter class specification
      Since:
      1.5
      See Also:

    • formatted

      public String formatted(Object... args)
      Formats using this string as the format string, and the supplied arguments.
      Implementation Requirements:
      This method is equivalent to String.format(this, args).
      Parameters:
      args - Arguments referenced by the format specifiers in this string.
      Returns:
      A formatted string
      Since:
      15
      See Also:

    • valueOf

      public static String valueOf(Object obj)
      Returns the string representation of the Object argument.
      Parameters:
      obj - an Object.
      Returns:
      if the argument is null, then a string equal to "null"; otherwise, the value of obj.toString() is returned.
      See Also:

    • valueOf

      public static String valueOf(char[] data)
      Returns the string representation of the char array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the returned string.
      Parameters:
      data - the character array.
      Returns:
      a String that contains the characters of the character array.

    • valueOf

      public static String valueOf(char[] data, int offset, int count)
      Returns the string representation of a specific subarray of the char array argument.

      The offset argument is the index of the first character of the subarray. The count argument specifies the length of the subarray. The contents of the subarray are copied; subsequent modification of the character array does not affect the returned string.

      Parameters:
      data - the character array.
      offset - initial offset of the subarray.
      count - length of the subarray.
      Returns:
      a String that contains the characters of the specified subarray of the character array.
      Throws:
      IndexOutOfBoundsException - if offset is negative, or count is negative, or offset+count is larger than data.length.

    • copyValueOf

      public static String copyValueOf(char[] data, int offset, int count)
      Equivalent to valueOf(char[], int, int).
      Parameters:
      data - the character array.
      offset - initial offset of the subarray.
      count - length of the subarray.
      Returns:
      a String that contains the characters of the specified subarray of the character array.
      Throws:
      IndexOutOfBoundsException - if offset is negative, or count is negative, or offset+count is larger than data.length.

    • copyValueOf

      public static String copyValueOf(char[] data)
      Equivalent to valueOf(char[]).
      Parameters:
      data - the character array.
      Returns:
      a String that contains the characters of the character array.

    • valueOf

      public static String valueOf(boolean b)
      Returns the string representation of the boolean argument.
      Parameters:
      b - a boolean.
      Returns:
      if the argument is true, a string equal to "true" is returned; otherwise, a string equal to "false" is returned.

    • valueOf

      public static String valueOf(char c)
      Returns the string representation of the char argument.
      Parameters:
      c - a char.
      Returns:
      a string of length 1 containing as its single character the argument c.

    • valueOf

      public static String valueOf(int i)
      Returns the string representation of the int argument.

      The representation is exactly the one returned by the Integer.toString method of one argument.

      Parameters:
      i - an int.
      Returns:
      a string representation of the int argument.
      See Also:

    • valueOf

      public static String valueOf(long l)
      Returns the string representation of the long argument.

      The representation is exactly the one returned by the Long.toString method of one argument.

      Parameters:
      l - a long.
      Returns:
      a string representation of the long argument.
      See Also:

    • valueOf

      public static String valueOf(float f)
      Returns the string representation of the float argument.

      The representation is exactly the one returned by the Float.toString method of one argument.

      Parameters:
      f - a float.
      Returns:
      a string representation of the float argument.
      See Also:

    • valueOf

      public static String valueOf(double d)
      Returns the string representation of the double argument.

      The representation is exactly the one returned by the Double.toString method of one argument.

      Parameters:
      d - a double.
      Returns:
      a string representation of the double argument.
      See Also:

    • intern

      public String intern()
      Returns a canonical representation for the string object.

      A pool of strings, initially empty, is maintained privately by the class String.

      When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

      It follows that for any two strings s and t, s.intern() == t.intern() is true if and only if s.equals(t) is true.

      All literal strings and string-valued constant expressions are interned. String literals are defined in section 3.10.5 of the The Java Language Specification.

      Returns:
      a string that has the same contents as this string, but is guaranteed to be from a pool of unique strings.

    • repeat

      public String repeat(int count)
      Returns a string whose value is the concatenation of this string repeated count times.

      If this string is empty or count is zero then the empty string is returned.

      Parameters:
      count - number of times to repeat
      Returns:
      A string composed of this string repeated count times or the empty string if this string is empty or count is zero
      Throws:
      IllegalArgumentException - if the count is negative.
      Since:
      11

    • describeConstable

      public Optional<String> describeConstable()
      Returns an Optional containing the nominal descriptor for this instance, which is the instance itself.
      Specified by:
      describeConstable in interface Constable
      Returns:
      an Optional describing the String instance
      Since:
      12

    • resolveConstantDesc

      public String resolveConstantDesc(MethodHandles.Lookup lookup)
      Resolves this instance as a ConstantDesc, the result of which is the instance itself.
      Specified by:
      resolveConstantDesc in interface ConstantDesc
      Parameters:
      lookup - ignored
      Returns:
      the String instance
      Since:
      12