de.caff.generics

Class HashCoder<T>

java.lang.Object

de.caff.generics.HashCoder<T>

Type Parameters:

T - type of hashed object

All Implemented Interfaces:

HashCodeCalculator<T>, Matcher<T,T>, UniformMatcher<T>, java.util.function.BiPredicate<T,T>

public class HashCoder<T>
extends java.lang.Object
implements HashCodeCalculator<T>, UniformMatcher<T>

Helper interface for HashCoderMap.

This class provides substitute hash values and equals implementation. To be null-safe all three arguments of HashCoder(HashCodeCalculator, Matcher, Function) need to be null-safe. The default implementations used in the constructors with fewer arguments are null-safe.

Since:

Mai 18, 2020

Author:

Rammi

Field Summary

Fields inherited from interface de.caff.generics.HashCodeCalculator

OBJECTS

Fields inherited from interface de.caff.generics.UniformMatcher

IDENTICAL

Constructor Summary

Constructors

Constructor and Description
HashCoder(java.util.function.Function<T,T> copier) Constructor.
HashCoder(HashCodeCalculator<? super T> codeCalculator) Constructor.
HashCoder(HashCodeCalculator<? super T> codeCalculator, Matcher<? super T,? super T> matcher) Constructor.
HashCoder(HashCodeCalculator<? super T> codeCalculator, Matcher<? super T,? super T> matcher, java.util.function.Function<T,T> copier) Constructor.

Method Summary

Modifier and Type	Method and Description
boolean	areEqual(T object1, T object2) Are the given two objects considered equal?
T	copy(T key) Copy a key.
int	getHashCode(T obj) Get the hash code value of the given object.
static <V> HashCoder<V>	natural() Get a fast natural hash coder using just the object's methods for hashing and equality, but not checking for null values.
static <V> HashCoder<V>	naturalNullSafe() Get a natural hash coder using just the object's methods for hashing and equality, allowing for null values.

Methods inherited from class java.lang.Object

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

Methods inherited from interface de.caff.generics.HashCodeCalculator

objects

Methods inherited from interface de.caff.generics.UniformMatcher

identical

Methods inherited from interface de.caff.generics.Matcher

foldLeft, foldRight, test

Methods inherited from interface java.util.function.BiPredicate

and, negate, or

Constructor Detail

HashCoder

public HashCoder(@NotNull
                 HashCodeCalculator<? super T> codeCalculator,
                 @NotNull
                 Matcher<? super T,? super T> matcher,
                 @NotNull
                 java.util.function.Function<T,T> copier)

Constructor.

Parameters:

codeCalculator - calculator for hash codes

matcher - equality checker

copier - copier for incoming and outgoing keys, useful to make keys immutable which is a basic requirements for hash keys

HashCoder

public HashCoder(@NotNull
                 HashCodeCalculator<? super T> codeCalculator,
                 @NotNull
                 Matcher<? super T,? super T> matcher)

Constructor.

This used simple copying for the keys.

Parameters:

codeCalculator - calculator for hash codes

matcher - equality checker

HashCoder

public HashCoder(@NotNull
                 HashCodeCalculator<? super T> codeCalculator)

Constructor. This uses Objects.equals(java.lang.Object, java.lang.Object) and simple copying for the keys.

Parameters:

codeCalculator - hash code calculator

HashCoder

public HashCoder(@NotNull
                 java.util.function.Function<T,T> copier)

Constructor. This is useful to decouple hash keys, allowing to use mutable objects for keys in a hash map or set. Obviuosly then the copier has to really copy the object.

Hashcode and equality checks are just using the standard implementation from the key objects.

Parameters:

copier - copier for incoming and outgoing keys

Method Detail

getHashCode

public int getHashCode(T obj)

Description copied from interface: HashCodeCalculator

Get the hash code value of the given object.

Specified by:

getHashCode in interface HashCodeCalculator<T>

Parameters:

obj - object for which the hash code is requested

Returns:

hash code

areEqual

public boolean areEqual(T object1,
                        T object2)

Description copied from interface: Matcher

Are the given two objects considered equal?

Specified by:

areEqual in interface Matcher<T,T>

Parameters:

object1 - first object

object2 - second object

Returns:

true if this matcher considers the two objects equal
false if this matcher considers them different

copy

public T copy(T key)

Copy a key.

Parameters:

key - key to copy

Returns:

copied key, possible the incoming one

natural

@NotNull
public static <V> HashCoder<V> natural()

Get a fast natural hash coder using just the object's methods for hashing and equality, but not checking for null values.

Specified by:

natural in interface HashCodeCalculator<T>

Specified by:

natural in interface UniformMatcher<T>

Type Parameters:

V - value type

Returns:

natural hash coder

naturalNullSafe

@NotNull
public static <V> HashCoder<V> naturalNullSafe()

Get a natural hash coder using just the object's methods for hashing and equality, allowing for null values.

Specified by:

naturalNullSafe in interface HashCodeCalculator<T>

Specified by:

naturalNullSafe in interface UniformMatcher<T>

Type Parameters:

V - value type

Returns:

natural hash coder