net.sf.classifier4J.util
Class CompareToBuilder

java.lang.Object
  |
  +--net.sf.classifier4J.util.CompareToBuilder

public class CompareToBuilder

extends java.lang.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 is a method reflectionCompare that uses 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,v 1.1 2005/02/04 05:30:28 nicklothian Exp $

Author:

Steve Downey, Stephen Colebourne, Gary Gregory, Pete Gieser

See Also:

Comparable, Object.equals(Object), Object.hashCode(), EqualsBuilder, HashCodeBuilder

Constructor Summary

CompareToBuilder()
Constructor for CompareToBuilder.

Method Summary

CompareToBuilder	append(boolean[] lhs, boolean[] rhs) Appends to the builder the deep comparison of two boolean arrays.
CompareToBuilder	append(boolean lhs, boolean rhs) Appends to the builder the comparison of two booleanss.
CompareToBuilder	append(byte[] lhs, byte[] rhs) Appends to the builder the deep comparison of two byte arrays.
CompareToBuilder	append(byte lhs, byte rhs) Appends to the builder the comparison of two bytes.
CompareToBuilder	append(char[] lhs, char[] rhs) Appends to the builder the deep comparison of two char arrays.
CompareToBuilder	append(char lhs, char rhs) Appends to the builder the comparison of two chars.
CompareToBuilder	append(double[] lhs, double[] rhs) Appends to the builder the deep comparison of two double arrays.
CompareToBuilder	append(double lhs, double rhs) Appends to the builder the comparison of two doubles.
CompareToBuilder	append(float[] lhs, float[] rhs) Appends to the builder the deep comparison of two float arrays.
CompareToBuilder	append(float lhs, float rhs) Appends to the builder the comparison of two floats.
CompareToBuilder	append(int[] lhs, int[] rhs) Appends to the builder the deep comparison of two int arrays.
CompareToBuilder	append(int lhs, int rhs) Appends to the builder the comparison of two ints.
CompareToBuilder	append(long[] lhs, long[] rhs) Appends to the builder the deep comparison of two long arrays.
CompareToBuilder	append(long lhs, long rhs) Appends to the builder the comparison of two longs.
CompareToBuilder	append(java.lang.Object[] lhs, java.lang.Object[] rhs) Appends to the builder the deep comparison of two Object arrays.
CompareToBuilder	append(java.lang.Object[] lhs, java.lang.Object[] rhs, java.util.Comparator comparator) Appends to the builder the deep comparison of two Object arrays.
CompareToBuilder	append(java.lang.Object lhs, java.lang.Object rhs) Appends to the builder the comparison of two Objects.
CompareToBuilder	append(java.lang.Object lhs, java.lang.Object rhs, java.util.Comparator comparator) Appends to the builder the comparison of two Objects.
CompareToBuilder	append(short[] lhs, short[] rhs) Appends to the builder the deep comparison of two short arrays.
CompareToBuilder	append(short lhs, short rhs) Appends to the builder the comparison of two shorts.
CompareToBuilder	appendSuper(int superCompareTo) Appends to the builder the compareTo(Object) result of the superclass.
static int	compare(double lhs, double rhs)
static int	reflectionCompare(java.lang.Object lhs, java.lang.Object rhs) Compares two Objects via reflection.
static int	reflectionCompare(java.lang.Object lhs, java.lang.Object rhs, boolean compareTransients) Compares two Objects via reflection.
static int	reflectionCompare(java.lang.Object lhs, java.lang.Object rhs, boolean compareTransients, java.lang.Class reflectUpToClass) Compares two Objects via reflection.
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.

Methods inherited from class java.lang.Object

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

Constructor Detail

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 Detail

reflectionCompare

public static int reflectionCompare(java.lang.Object lhs,
                                    java.lang.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:

java.lang.NullPointerException - if either (but not both) parameters are null

java.lang.ClassCastException - if rhs is not assignment-compatible with lhs

reflectionCompare

public static int reflectionCompare(java.lang.Object lhs,
                                    java.lang.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:

java.lang.NullPointerException - if either lhs or rhs (but not both) is null

java.lang.ClassCastException - if rhs is not assignment-compatible with lhs

reflectionCompare

public static int reflectionCompare(java.lang.Object lhs,
                                    java.lang.Object rhs,
                                    boolean compareTransients,
                                    java.lang.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:

java.lang.NullPointerException - if either lhs or rhs (but not both) is null

java.lang.ClassCastException - if rhs is not assignment-compatible with lhs

Since:

2.0

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(java.lang.Object lhs,
                               java.lang.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:

java.lang.ClassCastException - if rhs is not assignment-compatible with lhs

append

public CompareToBuilder append(java.lang.Object lhs,
                               java.lang.Object rhs,
                               java.util.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:

java.lang.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(java.lang.Object[] lhs,
                               java.lang.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:

java.lang.ClassCastException - if rhs is not assignment-compatible with lhs

append

public CompareToBuilder append(java.lang.Object[] lhs,
                               java.lang.Object[] rhs,
                               java.util.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:

java.lang.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

compare

public static int compare(double lhs,
                          double rhs)