com.helger.commons.hash

Class HashCodeGenerator

java.lang.Object

com.helger.commons.hash.HashCodeGenerator

All Implemented Interfaces:

IHashCodeGenerator, IAppendable<IHashCodeGenerator>

@NotThreadSafe
public final class HashCodeGenerator
extends Object
implements IHashCodeGenerator

A small hash code creation class based on the article found in the net. See this article for details.
After calling append(Object) for all objects use getHashCode() to retrieve the calculated hash code. Once the hash code was calculated no modifications are allowed.

A real world example for a final class derived from Object or a base class looks like this:

 @Override
 public int hashCode ()
 {
   return new HashCodeGenerator (this).append (member1).append (member2).getHashCode ();
 }
 

For a derived class, the typical code looks like this, assuming the base class also uses HashCodeGenerator:

 @Override
 public int hashCode ()
 {
   return HashCodeGenerator.getDerived (super.hashCode ()).append (member3).append (member4).getHashCode ();
 }
 

Author:

Philip Helger

Field Summary

Fields

Modifier and Type	Field and Description
static int	INITIAL_HASHCODE Use a prime number as the start.

Fields inherited from interface com.helger.commons.hash.IHashCodeGenerator

ILLEGAL_HASHCODE

Constructor Summary

Constructors

Constructor and Description
HashCodeGenerator(Class<?> aClass) This constructor requires a class name, because in case a class has no instance variables the hash code may be the same for different instances of different classes.
HashCodeGenerator(Object aSrcObject) This is a sanity constructor that allows for any object to be passed in the constructor (e.g.

Method Summary

Methods

Modifier and Type	Method and Description
HashCodeGenerator	append(boolean x) Atomic type hash code generation.
HashCodeGenerator	append(boolean[] x) Array hash code generation.
HashCodeGenerator	append(byte x) Atomic type hash code generation.
HashCodeGenerator	append(byte[] x) Array hash code generation.
HashCodeGenerator	append(char x) Atomic type hash code generation.
HashCodeGenerator	append(char[] x) Array hash code generation.
HashCodeGenerator	append(double x) Atomic type hash code generation.
HashCodeGenerator	append(double[] x) Array hash code generation.
HashCodeGenerator	append(Enum<?> x) Object hash code generation.
HashCodeGenerator	append(Enum<?>[] x) Array hash code generation.
HashCodeGenerator	append(float x) Atomic type hash code generation.
HashCodeGenerator	append(float[] x) Array hash code generation.
HashCodeGenerator	append(int x) Atomic type hash code generation.
HashCodeGenerator	append(int[] x) Array hash code generation.
HashCodeGenerator	append(Iterable<?> x)
HashCodeGenerator	append(long x) Atomic type hash code generation.
HashCodeGenerator	append(long[] x) Array hash code generation.
HashCodeGenerator	append(Map<?,?> x)
HashCodeGenerator	append(Node x)
HashCodeGenerator	append(Object x) Object hash code generation.
HashCodeGenerator	append(Object[] x) Array hash code generation.
HashCodeGenerator	append(short x) Atomic type hash code generation.
HashCodeGenerator	append(short[] x) Array hash code generation.
HashCodeGenerator	append(StringBuffer x) Type specific hash code generation because parameter class has no overloaded equals method.
HashCodeGenerator	append(StringBuilder x) Type specific hash code generation because parameter class has no overloaded equals method.
boolean	equals(Object o) Deprecated.
static HashCodeGenerator	getDerived(int nSuperHashCode) Create a HashCodeGenerator for derived classes where the base class also uses the HashCodeGenerator.
int	getHashCode() Retrieve the final hash code.
Integer	getHashCodeObj()
int	hashCode() Deprecated.

Methods inherited from class java.lang.Object

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

Field Detail

INITIAL_HASHCODE

public static final int INITIAL_HASHCODE

Use a prime number as the start.

See Also:

Constant Field Values

Constructor Detail

HashCodeGenerator

public HashCodeGenerator(@Nonnull
                 Object aSrcObject)

This is a sanity constructor that allows for any object to be passed in the constructor (e.g. this) from which the class is extracted as the initial value of the hash code.

Parameters:

aSrcObject - The source object from which the class is extracted. May not be null.

HashCodeGenerator

public HashCodeGenerator(@Nonnull
                 Class<?> aClass)

This constructor requires a class name, because in case a class has no instance variables the hash code may be the same for different instances of different classes.

Parameters:

aClass - The class this instance is about to create a hash code for. May not be null.

Method Detail

append

@Nonnull
public HashCodeGenerator append(boolean x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(byte x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(char x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(double x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(float x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(int x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(long x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(short x)

Atomic type hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Object x)

Object hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Enum<?> x)

Object hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               boolean[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               byte[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               char[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               double[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               float[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               int[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               long[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               short[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Object[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Enum<?>[] x)

Array hash code generation.

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               StringBuffer x)

Type specific hash code generation because parameter class has no overloaded equals method.

Parameters:

x - object to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               StringBuilder x)

Type specific hash code generation because parameter class has no overloaded equals method.

Parameters:

x - object to add

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Iterable<?> x)

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - to be included in the hash code generation.

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Map<?,?> x)

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - to be included in the hash code generation.

Returns:

this

append

@Nonnull
public HashCodeGenerator append(@Nullable
                               Node x)

Specified by:

append in interface IAppendable<IHashCodeGenerator>

Parameters:

x - to be included in the hash code generation.

Returns:

this

getHashCode

public int getHashCode()

Retrieve the final hash code. Once this method has been called, no further calls to append can be done since the hash value is locked!

Specified by:

getHashCode in interface IHashCodeGenerator

Returns:

The finally completed hash code. The returned value is never IHashCodeGenerator.ILLEGAL_HASHCODE. If the calculated hash code would be IHashCodeGenerator.ILLEGAL_HASHCODE it is changed to -1 instead.

getHashCodeObj

@Nonnull
public Integer getHashCodeObj()

Returns:

The same as getHashCode() but as an Integer object. Never null.

equals

@Deprecated
public boolean equals(Object o)

Deprecated.

Never compare HashCodeGenerator objects :)

Overrides:

equals in class Object

hashCode

@Deprecated
public int hashCode()

Deprecated.

Always use getHashCode()

Overrides:

hashCode in class Object

Returns:

getHashCode()

See Also:

getHashCode()

getDerived

@Nonnull
public static HashCodeGenerator getDerived(int nSuperHashCode)

Create a HashCodeGenerator for derived classes where the base class also uses the HashCodeGenerator. This avoid calculating the hash code of the class name more than once.

Parameters:

nSuperHashCode - Always pass in super.hashCode ()

Returns:

Never null