org.apache.commons.lang.builder
Class EqualsBuilder

java.lang.Object
  org.apache.commons.lang.builder.EqualsBuilder

public class EqualsBuilder

extends Object

Assists in implementing Object.equals(Object) methods.

This class provides methods to build a good equals method for any class. It follows rules laid out in Effective Java , by Joshua Bloch. In particular the rule for comparing doubles, floats, and arrays can be tricky. Also, making sure that equals() and hashCode() are consistent can be difficult.

Two Objects that compare as equals must generate the same hash code, but two Objects with the same hash code do not have to be equal.

All relevant fields should be included in the calculation of equals. Derived fields may be ignored. In particular, any field used in generating a hash code must be used in the equals method, and vice versa.

Typical use for the code is as follows:

 public boolean equals(Object obj) {
   if (obj instanceof MyClass == false) {
     return false;
   }
   if (this == obj) {
     return true;
   }
   MyClass rhs = (MyClass) obj;
   return new EqualsBuilder()
                 .appendSuper(super.equals(obj))
                 .append(field1, rhs.field1)
                 .append(field2, rhs.field2)
                 .append(field3, rhs.field3)
                 .isEquals();
  }
 

Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are usually private, the method, reflectionEquals, uses AccessibleObject.setAccessible to change the visibility of the fields. This will fail under a security manager, unless the appropriate permissions are set up correctly. It is also slower than testing explicitly.

A typical invocation for this method would look like:

 public boolean equals(Object obj) {
   return EqualsBuilder.reflectionEquals(this, obj);
 }
 

Since:

1.0

Version:

$Id: EqualsBuilder.java 161243 2005-04-14 04:30:28Z ggregory $

Author:

Steve Downey, Stephen Colebourne, Gary Gregory, Pete Gieser, Arun Mammen Thomas

Constructor Summary

EqualsBuilder()
Constructor for EqualsBuilder.

Method Summary

EqualsBuilder	append(boolean[] lhs, boolean[] rhs) Deep comparison of array of boolean.
EqualsBuilder	append(boolean lhs, boolean rhs) Test if two booleanss are equal.
EqualsBuilder	append(byte[] lhs, byte[] rhs) Deep comparison of array of byte.
EqualsBuilder	append(byte lhs, byte rhs) Test if two bytes are equal.
EqualsBuilder	append(char[] lhs, char[] rhs) Deep comparison of array of char.
EqualsBuilder	append(char lhs, char rhs) Test if two chars are equal.
EqualsBuilder	append(double[] lhs, double[] rhs) Deep comparison of array of double.
EqualsBuilder	append(double lhs, double rhs) Test if two doubles are equal by testing that the pattern of bits returned by doubleToLong are equal.
EqualsBuilder	append(float[] lhs, float[] rhs) Deep comparison of array of float.
EqualsBuilder	append(float lhs, float rhs) Test if two floats are equal byt testing that the pattern of bits returned by doubleToLong are equal.
EqualsBuilder	append(int[] lhs, int[] rhs) Deep comparison of array of int.
EqualsBuilder	append(int lhs, int rhs) Test if two ints are equal.
EqualsBuilder	append(long[] lhs, long[] rhs) Deep comparison of array of long.
EqualsBuilder	append(long lhs, long rhs) Test if two long s are equal.
EqualsBuilder	append(Object[] lhs, Object[] rhs) Performs a deep comparison of two Object arrays.
EqualsBuilder	append(Object lhs, Object rhs) Test if two Objects are equal using their equals method.
EqualsBuilder	append(short[] lhs, short[] rhs) Deep comparison of array of short.
EqualsBuilder	append(short lhs, short rhs) Test if two shorts are equal.
EqualsBuilder	appendSuper(boolean superEquals) Adds the result of super.equals() to this builder.
boolean	isEquals() Returns true if the fields that have been checked are all equal.
static boolean	reflectionEquals(Object lhs, Object rhs) This method uses reflection to determine if the two Objects are equal.
static boolean	reflectionEquals(Object lhs, Object rhs, boolean testTransients) This method uses reflection to determine if the two Objects are equal.
static boolean	reflectionEquals(Object lhs, Object rhs, boolean testTransients, Class reflectUpToClass) This method uses reflection to determine if the two Objects are equal.
protected void	setEquals(boolean isEquals) Sets the isEquals value.

Methods inherited from class java.lang.Object

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

Constructor Detail

EqualsBuilder

public EqualsBuilder()

Constructor for EqualsBuilder.

Starts off assuming that equals is true.

See Also:

Object.equals(Object)

Method Detail

reflectionEquals

public static boolean reflectionEquals(Object lhs,
                                       Object rhs)

This method uses reflection to determine if the two Objects are equal.

It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly.

Transient members will be not be tested, as they are likely derived fields, and not part of the value of the Object.

Static fields will not be tested. Superclass fields will be included.

Parameters:

lhs - this object

rhs - the other object

Returns:

true if the two Objects have tested equals.

reflectionEquals

public static boolean reflectionEquals(Object lhs,
                                       Object rhs,
                                       boolean testTransients)

This method uses reflection to determine if the two Objects are equal.

It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly.

If the TestTransients parameter is set to true, transient members will be tested, otherwise they are ignored, as they are likely derived fields, and not part of the value of the Object.

Static fields will not be tested. Superclass fields will be included.

Parameters:

lhs - this object

rhs - the other object

testTransients - whether to include transient fields

Returns:

true if the two Objects have tested equals.

reflectionEquals

public static boolean reflectionEquals(Object lhs,
                                       Object rhs,
                                       boolean testTransients,
                                       Class reflectUpToClass)

This method uses reflection to determine if the two Objects are equal.

It uses AccessibleObject.setAccessible to gain access to private fields. This means that it will throw a security exception if run under a security manager, if the permissions are not set up correctly. It is also not as efficient as testing explicitly.

If the testTransients parameter is set to true, transient members will be tested, otherwise they are ignored, as they are likely derived fields, and not part of the value of the Object.

Static fields will not be included. Superclass fields will be appended up to and including the specified superclass. A null superclass is treated as java.lang.Object.

Parameters:

lhs - this object

rhs - the other object

testTransients - whether to include transient fields

reflectUpToClass - the superclass to reflect up to (inclusive), may be null

Returns:

true if the two Objects have tested equals.

Since:

2.0

appendSuper

public EqualsBuilder appendSuper(boolean superEquals)

Adds the result of super.equals() to this builder.

Parameters:

superEquals - the result of calling super.equals()

Returns:

EqualsBuilder - used to chain calls.

Since:

2.0

append

public EqualsBuilder append(Object lhs,
                            Object rhs)

Test if two Objects are equal using their equals method.

Parameters:

lhs - the left hand object

rhs - the right hand object

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(long lhs,
                            long rhs)

Test if two long s are equal.

Parameters:

lhs - the left hand long

rhs - the right hand long

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(int lhs,
                            int rhs)

Test if two ints are equal.

Parameters:

lhs - the left hand int

rhs - the right hand int

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(short lhs,
                            short rhs)

Test if two shorts are equal.

Parameters:

lhs - the left hand short

rhs - the right hand short

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(char lhs,
                            char rhs)

Test if two chars are equal.

Parameters:

lhs - the left hand char

rhs - the right hand char

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(byte lhs,
                            byte rhs)

Test if two bytes are equal.

Parameters:

lhs - the left hand byte

rhs - the right hand byte

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(double lhs,
                            double rhs)

Test if two doubles are equal by testing that the pattern of bits returned by doubleToLong are equal.

This handles NaNs, Infinities, and -0.0.

It is compatible with the hash code generated by HashCodeBuilder.

Parameters:

lhs - the left hand double

rhs - the right hand double

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(float lhs,
                            float rhs)

Test if two floats are equal byt testing that the pattern of bits returned by doubleToLong are equal.

This handles NaNs, Infinities, and -0.0.

It is compatible with the hash code generated by HashCodeBuilder.

Parameters:

lhs - the left hand float

rhs - the right hand float

Returns:

EqualsBuilder - used to chain calls.

append

public EqualsBuilder append(boolean lhs,
                            boolean rhs)

Test if two booleanss are equal.

Parameters:

lhs - the left hand boolean

rhs - the right hand boolean

Returns:

EqualsBuilder - used to chain calls.

append

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

Performs a deep comparison of two Object arrays.

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

Parameters:

lhs - the left hand Object[]

rhs - the right hand Object[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of long. Length and all values are compared.

The method append(long, long) is used.

Parameters:

lhs - the left hand long[]

rhs - the right hand long[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of int. Length and all values are compared.

The method append(int, int) is used.

Parameters:

lhs - the left hand int[]

rhs - the right hand int[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of short. Length and all values are compared.

The method append(short, short) is used.

Parameters:

lhs - the left hand short[]

rhs - the right hand short[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of char. Length and all values are compared.

The method append(char, char) is used.

Parameters:

lhs - the left hand char[]

rhs - the right hand char[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of byte. Length and all values are compared.

The method append(byte, byte) is used.

Parameters:

lhs - the left hand byte[]

rhs - the right hand byte[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of double. Length and all values are compared.

The method append(double, double) is used.

Parameters:

lhs - the left hand double[]

rhs - the right hand double[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of float. Length and all values are compared.

The method append(float, float) is used.

Parameters:

lhs - the left hand float[]

rhs - the right hand float[]

Returns:

EqualsBuilder - used to chain calls.

append

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

Deep comparison of array of boolean. Length and all values are compared.

The method append(boolean, boolean) is used.

Parameters:

lhs - the left hand boolean[]

rhs - the right hand boolean[]

Returns:

EqualsBuilder - used to chain calls.

isEquals

public boolean isEquals()

Returns true if the fields that have been checked are all equal.

Returns:

boolean

setEquals

protected void setEquals(boolean isEquals)

Sets the isEquals value.

Parameters:

isEquals - The value to set.

Since:

2.1