com.helger.jcodemodel.util

Class JCHashCodeGenerator

java.lang.Object

com.helger.jcodemodel.util.JCHashCodeGenerator

@NotThreadSafe
public final class JCHashCodeGenerator
extends Object

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 JCHashCodeGenerator:

 @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	ILLEGAL_HASHCODE Represents an illegal hash code that is never to be returned!
static int	INITIAL_HASHCODE Use a prime number as the start.

Constructor Summary

Constructors

Constructor and Description
JCHashCodeGenerator(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.
JCHashCodeGenerator(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
JCHashCodeGenerator	append(boolean x) Atomic type hash code generation.
JCHashCodeGenerator	append(boolean[] x) Array hash code generation.
JCHashCodeGenerator	append(byte x) Atomic type hash code generation.
JCHashCodeGenerator	append(byte[] x) Array hash code generation.
JCHashCodeGenerator	append(char x) Atomic type hash code generation.
JCHashCodeGenerator	append(char[] x) Array hash code generation.
JCHashCodeGenerator	append(double x) Atomic type hash code generation.
JCHashCodeGenerator	append(double[] x) Array hash code generation.
JCHashCodeGenerator	append(Enum<?> x) Object hash code generation.
JCHashCodeGenerator	append(Enum<?>[] x) Array hash code generation.
JCHashCodeGenerator	append(float x) Atomic type hash code generation.
JCHashCodeGenerator	append(float[] x) Array hash code generation.
JCHashCodeGenerator	append(int x) Atomic type hash code generation.
JCHashCodeGenerator	append(int[] x) Array hash code generation.
JCHashCodeGenerator	append(Iterable<?> x)
JCHashCodeGenerator	append(long x) Atomic type hash code generation.
JCHashCodeGenerator	append(long[] x) Array hash code generation.
JCHashCodeGenerator	append(Map<?,?> x)
JCHashCodeGenerator	append(Node x)
JCHashCodeGenerator	append(Object x) Object hash code generation.
JCHashCodeGenerator	append(Object[] x) Array hash code generation.
JCHashCodeGenerator	append(short x) Atomic type hash code generation.
JCHashCodeGenerator	append(short[] x) Array hash code generation.
JCHashCodeGenerator	append(StringBuffer x) Type specific hash code generation because parameter class has no overloaded equals method.
JCHashCodeGenerator	append(StringBuilder x) Type specific hash code generation because parameter class has no overloaded equals method.
boolean	equals(Object o) Deprecated.
static JCHashCodeGenerator	getDerived(int nSuperHashCode) Create a JCHashCodeGenerator for derived classes where the base class also uses the JCHashCodeGenerator.
int	getHashCode() Retrieve the final hash code.
static int	getHashCode(int nSuperHashCode, Object... aMembers) Static helper method to create the hashcode of an object with a single invocation.
static int	getHashCode(Object aThis, Object... aMembers) Static helper method to create the hashcode of an object with a single invocation.
Integer	getHashCodeObj()
int	hashCode() Deprecated.

Methods inherited from class java.lang.Object

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

Field Detail

ILLEGAL_HASHCODE

public static final int ILLEGAL_HASHCODE

Represents an illegal hash code that is never to be returned!

See Also:

Constant Field Values

INITIAL_HASHCODE

public static final int INITIAL_HASHCODE

Use a prime number as the start.

See Also:

Constant Field Values

Constructor Detail

JCHashCodeGenerator

public JCHashCodeGenerator(@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.

JCHashCodeGenerator

public JCHashCodeGenerator(@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 JCHashCodeGenerator append(boolean x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(byte x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(char x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(double x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(float x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(int x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(long x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(short x)

Atomic type hash code generation.

Parameters:

x - Array to add

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(@Nullable
                                 Object x)

Object hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Object hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Array hash code generation.

Parameters:

x - Array to add

Returns:

this

append

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

Parameters:

x - to be included in the hash code generation.

Returns:

this

append

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

Parameters:

x - to be included in the hash code generation.

Returns:

this

append

@Nonnull
public JCHashCodeGenerator append(@Nullable
                                 Node x)

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!

Returns:

The finally completed hash code. The returned value is never ILLEGAL_HASHCODE. If the calculated hash code would be 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 JCHashCodeGenerator 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 JCHashCodeGenerator getDerived(int nSuperHashCode)

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

Parameters:

nSuperHashCode - Always pass in super.hashCode ()

Returns:

Never null

getHashCode

public static int getHashCode(@Nonnull
              Object aThis,
              @Nullable
              Object... aMembers)

Static helper method to create the hashcode of an object with a single invocation. This method must be used by objects that directly derive from Object.

Parameters:

aThis - this

aMembers - A list of all members. Primitive types must be boxed.

Returns:

The generated hashCode.

getHashCode

public static int getHashCode(@Nonnull
              int nSuperHashCode,
              @Nullable
              Object... aMembers)

Static helper method to create the hashcode of an object with a single invocation. This method must be used by objects that derive from a class other than Object.

Parameters:

nSuperHashCode - The result of super.hashCode()

aMembers - A list of all members. Primitive types must be boxed.

Returns:

The generated hashCode.