org.apache.commons.lang.builder
クラス HashCodeBuilder

java.lang.Object
  拡張org.apache.commons.lang.builder.HashCodeBuilder

public class HashCodeBuilder
extends Object

Assists in implementing Object.hashCode() methods.

This class enables a good hashCode method to be built for any class. It follows the rules laid out in the book Effective Java by Joshua Bloch. Writing a good hashCode method is actually quite difficult. This class aims to simplify the process.

All relevant fields from the object should be included in the hashCode method. Derived fields may be excluded. In general, any field used in the equals method must be used in the hashCode method.

To use this class write code as follows:

 public class Person {
   String name;
   int age;
   boolean isSmoker;
   ...

   public int hashCode() {
     // you pick a hard-coded, randomly chosen, non-zero, odd number
     // ideally different for each class
     return new HashCodeBuilder(17, 37).
       append(name).
       append(age).
       append(smoker).
       toHashCode();
   }
 }
 

If required, the superclass hashCode() can be added using appendSuper(int).

Alternatively, there is a method that uses reflection to determine the fields to test. Because these fields are usually private, the method, reflectionHashCode, 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 int hashCode() {
   return HashCodeBuilder.reflectionHashCode(this);
 }
 

導入されたバージョン:
1.0
バージョン:
$Id: HashCodeBuilder.java,v 1.1.1.1 2004/02/13 10:02:06 hioki Exp $
作成者:
Stephen Colebourne, Gary Gregory, Pete Gieser

コンストラクタの概要
HashCodeBuilder()
          Constructor.
HashCodeBuilder(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber)
          Constructor.
 
メソッドの概要
 HashCodeBuilder append(boolean value)
          Append a hashCode for a boolean.
 HashCodeBuilder append(boolean[] array)
          Append a hashCode for a boolean array.
 HashCodeBuilder append(byte value)
          Append a hashCode for a byte.
 HashCodeBuilder append(byte[] array)
          Append a hashCode for a byte array.
 HashCodeBuilder append(char value)
          Append a hashCode for a char.
 HashCodeBuilder append(char[] array)
          Append a hashCode for a char array.
 HashCodeBuilder append(double value)
          Append a hashCode for a double.
 HashCodeBuilder append(double[] array)
          Append a hashCode for a double array.
 HashCodeBuilder append(float value)
          Append a hashCode for a float.
 HashCodeBuilder append(float[] array)
          Append a hashCode for a float array.
 HashCodeBuilder append(int value)
          Append a hashCode for an int.
 HashCodeBuilder append(int[] array)
          Append a hashCode for an int array.
 HashCodeBuilder append(long value)
          Append a hashCode for a long.
 HashCodeBuilder append(long[] array)
          Append a hashCode for a long array.
 HashCodeBuilder append(Object object)
          Append a hashCode for an Object.
 HashCodeBuilder append(Object[] array)
          Append a hashCode for an Object array.
 HashCodeBuilder append(short value)
          Append a hashCode for a short.
 HashCodeBuilder append(short[] array)
          Append a hashCode for a short array.
 HashCodeBuilder appendSuper(int superHashCode)
          Adds the result of super.hashCode() to this builder.
static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object)
          This method uses reflection to build a valid hash code.
static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object, boolean testTransients)
          This method uses reflection to build a valid hash code.
static int reflectionHashCode(int initialNonZeroOddNumber, int multiplierNonZeroOddNumber, Object object, boolean testTransients, Class reflectUpToClass)
          This method uses reflection to build a valid hash code.
static int reflectionHashCode(Object object)
          This method uses reflection to build a valid hash code.
static int reflectionHashCode(Object object, boolean testTransients)
          This method uses reflection to build a valid hash code.
 int toHashCode()
          Return the computed hashCode.
 
クラス java.lang.Object から継承したメソッド
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

コンストラクタの詳細

HashCodeBuilder

public HashCodeBuilder()

Constructor.

This constructor uses two hard coded choices for the constants needed to build a hashCode.


HashCodeBuilder

public HashCodeBuilder(int initialNonZeroOddNumber,
                       int multiplierNonZeroOddNumber)

Constructor.

Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class, however this is not vital.

Prime numbers are preferred, especially for the multiplier.

パラメータ:
initialNonZeroOddNumber - a non-zero, odd number used as the initial value
multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
例外:
IllegalArgumentException - if the number is zero or even
メソッドの詳細

reflectionHashCode

public static int reflectionHashCode(Object object)

This method uses reflection to build a valid hash code.

This constructor uses two hard coded choices for the constants needed to build a hash code.

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 used, 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.

パラメータ:
object - the Object to create a hashCode for
戻り値:
int hash code
例外:
IllegalArgumentException - if the object is null

reflectionHashCode

public static int reflectionHashCode(Object object,
                                     boolean testTransients)

This method uses reflection to build a valid hash code.

This constructor uses two hard coded choices for the constants needed to build a hash code.

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.

パラメータ:
object - the Object to create a hashCode for
testTransients - whether to include transient fields
戻り値:
int hash code
例外:
IllegalArgumentException - if the object is null

reflectionHashCode

public static int reflectionHashCode(int initialNonZeroOddNumber,
                                     int multiplierNonZeroOddNumber,
                                     Object object)

This method uses reflection to build a valid hash code.

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 used, 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.

Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class, however this is not vital. Prime numbers are preferred, especially for the multiplier.

パラメータ:
initialNonZeroOddNumber - a non-zero, odd number used as the initial value
multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
object - the Object to create a hashCode for
戻り値:
int hash code
例外:
IllegalArgumentException - if the Object is null
IllegalArgumentException - if the number is zero or even

reflectionHashCode

public static int reflectionHashCode(int initialNonZeroOddNumber,
                                     int multiplierNonZeroOddNumber,
                                     Object object,
                                     boolean testTransients)

This method uses reflection to build a valid hash code.

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.

Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class, however this is not vital. Prime numbers are preferred, especially for the multiplier.

パラメータ:
initialNonZeroOddNumber - a non-zero, odd number used as the initial value
multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
object - the Object to create a hashCode for
testTransients - whether to include transient fields
戻り値:
int hash code
例外:
IllegalArgumentException - if the Object is null
IllegalArgumentException - if the number is zero or even

reflectionHashCode

public static int reflectionHashCode(int initialNonZeroOddNumber,
                                     int multiplierNonZeroOddNumber,
                                     Object object,
                                     boolean testTransients,
                                     Class reflectUpToClass)

This method uses reflection to build a valid hash code.

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 included up to and including the specified superclass. A null superclass is treated as java.lang.Object.

Two randomly chosen, non-zero, odd numbers must be passed in. Ideally these should be different for each class, however this is not vital. Prime numbers are preferred, especially for the multiplier.

パラメータ:
initialNonZeroOddNumber - a non-zero, odd number used as the initial value
multiplierNonZeroOddNumber - a non-zero, odd number used as the multiplier
object - the Object to create a hashCode for
testTransients - whether to include transient fields
reflectUpToClass - the superclass to reflect up to (inclusive), may be null
戻り値:
int hash code
例外:
IllegalArgumentException - if the Object is null
IllegalArgumentException - if the number is zero or even
導入されたバージョン:
2.0

appendSuper

public HashCodeBuilder appendSuper(int superHashCode)

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

パラメータ:
superHashCode - the result of calling super.hashCode()
戻り値:
this HashCodeBuilder, used to chain calls.
導入されたバージョン:
2.0

append

public HashCodeBuilder append(Object object)

Append a hashCode for an Object.

パラメータ:
object - the Object to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(long value)

Append a hashCode for a long.

パラメータ:
value - the long to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(int value)

Append a hashCode for an int.

パラメータ:
value - the int to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(short value)

Append a hashCode for a short.

パラメータ:
value - the short to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(char value)

Append a hashCode for a char.

パラメータ:
value - the char to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(byte value)

Append a hashCode for a byte.

パラメータ:
value - the byte to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(double value)

Append a hashCode for a double.

パラメータ:
value - the double to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(float value)

Append a hashCode for a float.

パラメータ:
value - the float to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(boolean value)

Append a hashCode for a boolean.

パラメータ:
value - the boolean to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(Object[] array)

Append a hashCode for an Object array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(long[] array)

Append a hashCode for a long array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(int[] array)

Append a hashCode for an int array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(short[] array)

Append a hashCode for a short array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(char[] array)

Append a hashCode for a char array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(byte[] array)

Append a hashCode for a byte array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(double[] array)

Append a hashCode for a double array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(float[] array)

Append a hashCode for a float array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

append

public HashCodeBuilder append(boolean[] array)

Append a hashCode for a boolean array.

パラメータ:
array - the array to add to the hashCode
戻り値:
this

toHashCode

public int toHashCode()

Return the computed hashCode.

戻り値:
hashCode based on the fields appended


このドキュメントは、Ja-Jakartaにより訳されました。 コメントがある場合は report@jajakarta.orgまでお願いします。
Translated into Japanese by jajakarta.org. The original page is here.
Copyright (c) 2002-2003 - Apache Software Foundation