Module java.base
Package java.io

Class PushbackInputStream

java.lang.Object
java.io.InputStream
java.io.FilterInputStream
java.io.PushbackInputStream
All Implemented Interfaces:
Closeable, AutoCloseable
public class PushbackInputStream extends FilterInputStream
A PushbackInputStream adds functionality to another input stream, namely the ability to "push back" or "unread" bytes, by storing pushed-back bytes in an internal buffer. This is useful in situations where it is convenient for a fragment of code to read an indefinite number of data bytes that are delimited by a particular byte value; after reading the terminating byte, the code fragment can "unread" it, so that the next read operation on the input stream will reread the byte that was pushed back. For example, bytes representing the characters constituting an identifier might be terminated by a byte representing an operator character; a method whose job is to read just an identifier can read until it sees the operator and then push the operator back to be re-read.
Since:
1.0

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    protected byte[]
    buf
    The pushback buffer.
    protected int
    pos
    The position within the pushback buffer from which the next byte will be read.

    Fields declared in class java.io.FilterInputStream

    in

  • Constructor Summary

    Constructors
    Constructor
    Description
    PushbackInputStream(InputStream in)
    Creates a PushbackInputStream with a 1-byte pushback buffer, and saves its argument, the input stream in, for later use.
    PushbackInputStream(InputStream in, int size)
    Creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream in, for later use.

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    available()
    Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
    void
    close()
    Closes this input stream and releases any system resources associated with the stream.
    void
    mark(int readlimit)
    Marks the current position in this input stream.
    boolean
    markSupported()
    Tests if this input stream supports the mark and reset methods, which it does not.
    int
    read()
    Reads the next byte of data from this input stream.
    int
    read(byte[] b, int off, int len)
    Reads up to len bytes of data from this input stream into an array of bytes.
    void
    reset()
    Repositions this stream to the position at the time the mark method was last called on this input stream.
    long
    skip(long n)
    Skips over and discards n bytes of data from this input stream.
    void
    unread(byte[] b)
    Pushes back an array of bytes by copying it to the front of the pushback buffer.
    void
    unread(byte[] b, int off, int len)
    Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer.
    void
    unread(int b)
    Pushes back a byte by copying it to the front of the pushback buffer.

    Methods declared in class java.io.FilterInputStream

    read

    Methods declared in class java.io.InputStream

    nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo

    Methods declared in class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • buf

      protected byte[] buf
      The pushback buffer.
      Since:
      1.1

    • pos

      protected int pos
      The position within the pushback buffer from which the next byte will be read. When the buffer is empty, pos is equal to buf.length; when the buffer is full, pos is equal to zero.
      Since:
      1.1

  • Constructor Details

    • PushbackInputStream

      public PushbackInputStream(InputStream in, int size)
      Creates a PushbackInputStream with a pushback buffer of the specified size, and saves its argument, the input stream in, for later use. Initially, the pushback buffer is empty.
      Parameters:
      in - the input stream from which bytes will be read.
      size - the size of the pushback buffer.
      Throws:
      IllegalArgumentException - if size <= 0
      Since:
      1.1

    • PushbackInputStream

      public PushbackInputStream(InputStream in)
      Creates a PushbackInputStream with a 1-byte pushback buffer, and saves its argument, the input stream in, for later use. Initially, the pushback buffer is empty.
      Parameters:
      in - the input stream from which bytes will be read.

  • Method Details

    • read

      public int read() throws IOException
      Reads the next byte of data from this input stream. The value byte is returned as an int in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value -1 is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.

      This method returns the most recently pushed-back byte, if there is one, and otherwise calls the read method of its underlying input stream and returns whatever value that method returns.

      Overrides:
      read in class FilterInputStream
      Returns:
      the next byte of data, or -1 if the end of the stream has been reached.
      Throws:
      IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
      See Also:

    • read

      public int read(byte[] b, int off, int len) throws IOException
      Reads up to len bytes of data from this input stream into an array of bytes. This method first reads any pushed-back bytes; after that, if fewer than len bytes have been read then it reads from the underlying input stream. If len is not zero, the method blocks until at least 1 byte of input is available; otherwise, no bytes are read and 0 is returned.
      Overrides:
      read in class FilterInputStream
      Parameters:
      b - the buffer into which the data is read.
      off - the start offset in the destination array b
      len - the maximum number of bytes read.
      Returns:
      the total number of bytes read into the buffer, or -1 if there is no more data because the end of the stream has been reached.
      Throws:
      NullPointerException - If b is null.
      IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off
      IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
      See Also:

    • unread

      public void unread(int b) throws IOException
      Pushes back a byte by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value (byte)b.
      Parameters:
      b - the int value whose low-order byte is to be pushed back.
      Throws:
      IOException - If there is not enough room in the pushback buffer for the byte, or this input stream has been closed by invoking its close() method.

    • unread

      public void unread(byte[] b, int off, int len) throws IOException
      Pushes back a portion of an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[off], the byte after that will have the value b[off+1], and so forth.
      Parameters:
      b - the byte array to push back.
      off - the start offset of the data.
      len - the number of bytes to push back.
      Throws:
      NullPointerException - If b is null.
      IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.
      Since:
      1.1

    • unread

      public void unread(byte[] b) throws IOException
      Pushes back an array of bytes by copying it to the front of the pushback buffer. After this method returns, the next byte to be read will have the value b[0], the byte after that will have the value b[1], and so forth.
      Parameters:
      b - the byte array to push back
      Throws:
      NullPointerException - If b is null.
      IOException - If there is not enough room in the pushback buffer for the specified number of bytes, or this input stream has been closed by invoking its close() method.
      Since:
      1.1

    • available

      public int available() throws IOException
      Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

      The method returns the sum of the number of bytes that have been pushed back and the value returned by available.

      Overrides:
      available in class FilterInputStream
      Returns:
      the number of bytes that can be read (or skipped over) from the input stream without blocking.
      Throws:
      IOException - if this input stream has been closed by invoking its close() method, or an I/O error occurs.
      See Also:

    • skip

      public long skip(long n) throws IOException
      Skips over and discards n bytes of data from this input stream. The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly zero. If n is negative, no bytes are skipped.

      The skip method of PushbackInputStream first skips over the bytes in the pushback buffer, if any. It then calls the skip method of the underlying input stream if more bytes need to be skipped. The actual number of bytes skipped is returned.

      Overrides:
      skip in class FilterInputStream
      Parameters:
      n - the number of bytes to be skipped.
      Returns:
      the actual number of bytes skipped.
      Throws:
      IOException - if the stream has been closed by invoking its close() method, in.skip(n) throws an IOException, or an I/O error occurs.
      Since:
      1.2
      See Also:

    • markSupported

      public boolean markSupported()
      Tests if this input stream supports the mark and reset methods, which it does not.
      Overrides:
      markSupported in class FilterInputStream
      Returns:
      false, since this class does not support the mark and reset methods.
      See Also:

    • mark

      public void mark(int readlimit)
      Marks the current position in this input stream.

      The mark method of PushbackInputStream does nothing.

      Overrides:
      mark in class FilterInputStream
      Parameters:
      readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.
      See Also:

    • reset

      public void reset() throws IOException
      Repositions this stream to the position at the time the mark method was last called on this input stream.

      The method reset for class PushbackInputStream does nothing except throw an IOException.

      Overrides:
      reset in class FilterInputStream
      Throws:
      IOException - if this method is invoked.
      See Also:

    • close

      public void close() throws IOException
      Closes this input stream and releases any system resources associated with the stream. Once the stream has been closed, further read(), unread(), available(), reset(), or skip() invocations will throw an IOException. Closing a previously closed stream has no effect.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Overrides:
      close in class FilterInputStream
      Throws:
      IOException - if an I/O error occurs.
      See Also: