Package org.apache.commons.lang.builder

Class CompareToBuilder

java.lang.Object
org.apache.commons.lang.builder.CompareToBuilder
public class CompareToBuilder extends Object
Assists in implementing Comparable.compareTo(Object) methods. It is consistent with equals(Object) and hashcode() built with EqualsBuilder and HashCodeBuilder.

Two Objects that compare equal using equals(Object) should normally also compare equal using compareTo(Object).

All relevant fields should be included in the calculation of the comparison. Derived fields may be ignored. The same fields, in the same order, should be used in both compareTo(Object) and equals(Object).

To use this class write code as follows:

 public class MyClass {
   String field1;
   int field2;
   boolean field3;

   ...

   public int compareTo(Object o) {
     MyClass myClass = (MyClass) o;
     return new CompareToBuilder()
       .appendSuper(super.compareTo(o)
       .append(this.field1, myClass.field1)
       .append(this.field2, myClass.field2)
       .append(this.field3, myClass.field3)
       .toComparison();
   }
 }

Alternatively, there are reflectionCompare methods that use reflection to determine the fields to append. Because fields can be private, reflectionCompare uses AccessibleObject.setAccessible(boolean) to bypass normal access control checks. This will fail under a security manager, unless the appropriate permissions are set up correctly. It is also slower than appending explicitly.

A typical implementation of compareTo(Object) using reflectionCompare looks like:

 public int compareTo(Object o) {
   return CompareToBuilder.reflectionCompare(this, o);
 }
Since:
1.0
Version:
$Id: CompareToBuilder.java 1056843 2011-01-09 00:29:01Z niallp $
See Also:

  • Constructor Details

    • CompareToBuilder

      public CompareToBuilder()

      Constructor for CompareToBuilder.

      Starts off assuming that the objects are equal. Multiple calls are then made to the various append methods, followed by a call to toComparison() to get the result.

  • Method Details

    • reflectionCompare

      public static int reflectionCompare(Object lhs, Object rhs)

      Compares two Objects via reflection.

      Fields can be private, thus AccessibleObject.setAccessible is used to bypass normal access control checks. This will fail under a security manager unless the appropriate permissions are set.

      • Static fields will not be compared
      • Transient members will be not be compared, as they are likely derived fields
      • Superclass fields will be compared

      If both lhs and rhs are null, they are considered equal.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      Returns:
      a negative integer, zero, or a positive integer as lhs is less than, equal to, or greater than rhs
      Throws:
      NullPointerException - if either (but not both) parameters are null
      ClassCastException - if rhs is not assignment-compatible with lhs

    • reflectionCompare

      public static int reflectionCompare(Object lhs, Object rhs, boolean compareTransients)

      Compares two Objects via reflection.

      Fields can be private, thus AccessibleObject.setAccessible is used to bypass normal access control checks. This will fail under a security manager unless the appropriate permissions are set.

      • Static fields will not be compared
      • If compareTransients is true, compares transient members. Otherwise ignores them, as they are likely derived fields.
      • Superclass fields will be compared

      If both lhs and rhs are null, they are considered equal.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      compareTransients - whether to compare transient fields
      Returns:
      a negative integer, zero, or a positive integer as lhs is less than, equal to, or greater than rhs
      Throws:
      NullPointerException - if either lhs or rhs (but not both) is null
      ClassCastException - if rhs is not assignment-compatible with lhs

    • reflectionCompare

      public static int reflectionCompare(Object lhs, Object rhs, Collection excludeFields)

      Compares two Objects via reflection.

      Fields can be private, thus AccessibleObject.setAccessible is used to bypass normal access control checks. This will fail under a security manager unless the appropriate permissions are set.

      • Static fields will not be compared
      • If compareTransients is true, compares transient members. Otherwise ignores them, as they are likely derived fields.
      • Superclass fields will be compared

      If both lhs and rhs are null, they are considered equal.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      excludeFields - Collection of String fields to exclude
      Returns:
      a negative integer, zero, or a positive integer as lhs is less than, equal to, or greater than rhs
      Throws:
      NullPointerException - if either lhs or rhs (but not both) is null
      ClassCastException - if rhs is not assignment-compatible with lhs
      Since:
      2.2

    • reflectionCompare

      public static int reflectionCompare(Object lhs, Object rhs, String[] excludeFields)

      Compares two Objects via reflection.

      Fields can be private, thus AccessibleObject.setAccessible is used to bypass normal access control checks. This will fail under a security manager unless the appropriate permissions are set.

      • Static fields will not be compared
      • If compareTransients is true, compares transient members. Otherwise ignores them, as they are likely derived fields.
      • Superclass fields will be compared

      If both lhs and rhs are null, they are considered equal.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      excludeFields - array of fields to exclude
      Returns:
      a negative integer, zero, or a positive integer as lhs is less than, equal to, or greater than rhs
      Throws:
      NullPointerException - if either lhs or rhs (but not both) is null
      ClassCastException - if rhs is not assignment-compatible with lhs
      Since:
      2.2

    • reflectionCompare

      public static int reflectionCompare(Object lhs, Object rhs, boolean compareTransients, Class reflectUpToClass)

      Compares two Objects via reflection.

      Fields can be private, thus AccessibleObject.setAccessible is used to bypass normal access control checks. This will fail under a security manager unless the appropriate permissions are set.

      • Static fields will not be compared
      • If the compareTransients is true, compares transient members. Otherwise ignores them, as they are likely derived fields.
      • Compares superclass fields up to and including reflectUpToClass. If reflectUpToClass is null, compares all superclass fields.

      If both lhs and rhs are null, they are considered equal.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      compareTransients - whether to compare transient fields
      reflectUpToClass - last superclass for which fields are compared
      Returns:
      a negative integer, zero, or a positive integer as lhs is less than, equal to, or greater than rhs
      Throws:
      NullPointerException - if either lhs or rhs (but not both) is null
      ClassCastException - if rhs is not assignment-compatible with lhs
      Since:
      2.0

    • reflectionCompare

      public static int reflectionCompare(Object lhs, Object rhs, boolean compareTransients, Class reflectUpToClass, String[] excludeFields)

      Compares two Objects via reflection.

      Fields can be private, thus AccessibleObject.setAccessible is used to bypass normal access control checks. This will fail under a security manager unless the appropriate permissions are set.

      • Static fields will not be compared
      • If the compareTransients is true, compares transient members. Otherwise ignores them, as they are likely derived fields.
      • Compares superclass fields up to and including reflectUpToClass. If reflectUpToClass is null, compares all superclass fields.

      If both lhs and rhs are null, they are considered equal.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      compareTransients - whether to compare transient fields
      reflectUpToClass - last superclass for which fields are compared
      excludeFields - fields to exclude
      Returns:
      a negative integer, zero, or a positive integer as lhs is less than, equal to, or greater than rhs
      Throws:
      NullPointerException - if either lhs or rhs (but not both) is null
      ClassCastException - if rhs is not assignment-compatible with lhs
      Since:
      2.2

    • appendSuper

      public CompareToBuilder appendSuper(int superCompareTo)

      Appends to the builder the compareTo(Object) result of the superclass.

      Parameters:
      superCompareTo - result of calling super.compareTo(Object)
      Returns:
      this - used to chain append calls
      Since:
      2.0

    • append

      public CompareToBuilder append(Object lhs, Object rhs)

      Appends to the builder the comparison of two Objects.

      1. Check if lhs == rhs
      2. Check if either lhs or rhs is null, a null object is less than a non-null object
      3. Check the object contents

      lhs must either be an array or implement Comparable.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      Returns:
      this - used to chain append calls
      Throws:
      ClassCastException - if rhs is not assignment-compatible with lhs

    • append

      public CompareToBuilder append(Object lhs, Object rhs, Comparator comparator)

      Appends to the builder the comparison of two Objects.

      1. Check if lhs == rhs
      2. Check if either lhs or rhs is null, a null object is less than a non-null object
      3. Check the object contents

      If lhs is an array, array comparison methods will be used. Otherwise comparator will be used to compare the objects. If comparator is null, lhs must implement Comparable instead.

      Parameters:
      lhs - left-hand object
      rhs - right-hand object
      comparator - Comparator used to compare the objects, null means treat lhs as Comparable
      Returns:
      this - used to chain append calls
      Throws:
      ClassCastException - if rhs is not assignment-compatible with lhs
      Since:
      2.0

    • append

      public CompareToBuilder append(long lhs, long rhs)
      Appends to the builder the comparison of two longs.
      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(int lhs, int rhs)
      Appends to the builder the comparison of two ints.
      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(short lhs, short rhs)
      Appends to the builder the comparison of two shorts.
      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(char lhs, char rhs)
      Appends to the builder the comparison of two chars.
      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(byte lhs, byte rhs)
      Appends to the builder the comparison of two bytes.
      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(double lhs, double rhs)

      Appends to the builder the comparison of two doubles.

      This handles NaNs, Infinities, and -0.0.

      It is compatible with the hash code generated by HashCodeBuilder.

      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(float lhs, float rhs)

      Appends to the builder the comparison of two floats.

      This handles NaNs, Infinities, and -0.0.

      It is compatible with the hash code generated by HashCodeBuilder.

      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(boolean lhs, boolean rhs)
      Appends to the builder the comparison of two booleanss.
      Parameters:
      lhs - left-hand value
      rhs - right-hand value
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(Object[] lhs, Object[] rhs)

      Appends to the builder the deep comparison of two Object arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a short length array is less than a long length array
      4. Check array contents element by element using append(Object, Object, Comparator)

      This method will also will be called for the top level of multi-dimensional, ragged, and multi-typed arrays.

      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls
      Throws:
      ClassCastException - if rhs is not assignment-compatible with lhs

    • append

      public CompareToBuilder append(Object[] lhs, Object[] rhs, Comparator comparator)

      Appends to the builder the deep comparison of two Object arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a short length array is less than a long length array
      4. Check array contents element by element using append(Object, Object, Comparator)

      This method will also will be called for the top level of multi-dimensional, ragged, and multi-typed arrays.

      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      comparator - Comparator to use to compare the array elements, null means to treat lhs elements as Comparable.
      Returns:
      this - used to chain append calls
      Throws:
      ClassCastException - if rhs is not assignment-compatible with lhs
      Since:
      2.0

    • append

      public CompareToBuilder append(long[] lhs, long[] rhs)

      Appends to the builder the deep comparison of two long arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(long, long)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(int[] lhs, int[] rhs)

      Appends to the builder the deep comparison of two int arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(int, int)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(short[] lhs, short[] rhs)

      Appends to the builder the deep comparison of two short arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(short, short)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(char[] lhs, char[] rhs)

      Appends to the builder the deep comparison of two char arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(char, char)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(byte[] lhs, byte[] rhs)

      Appends to the builder the deep comparison of two byte arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(byte, byte)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(double[] lhs, double[] rhs)

      Appends to the builder the deep comparison of two double arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(double, double)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(float[] lhs, float[] rhs)

      Appends to the builder the deep comparison of two float arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(float, float)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • append

      public CompareToBuilder append(boolean[] lhs, boolean[] rhs)

      Appends to the builder the deep comparison of two boolean arrays.

      1. Check if arrays are the same using ==
      2. Check if for null, null is less than non-null
      3. Check array length, a shorter length array is less than a longer length array
      4. Check array contents element by element using append(boolean, boolean)
      Parameters:
      lhs - left-hand array
      rhs - right-hand array
      Returns:
      this - used to chain append calls

    • toComparison

      public int toComparison()
      Returns a negative integer, a positive integer, or zero as the builder has judged the "left-hand" side as less than, greater than, or equal to the "right-hand" side.
      Returns:
      final comparison result