org.apache.commons.functor.core
Class Constant<T>

java.lang.Object
  org.apache.commons.functor.core.Constant<T>

Type Parameters:

T - the returned value type.

All Implemented Interfaces:

Serializable, BinaryFunction<Object,Object,T>, BinaryFunctor<Object,Object>, BinaryPredicate<Object,Object>, Function<T>, Functor, NullaryFunctor, Predicate, UnaryFunction<Object,T>, UnaryFunctor<Object>, UnaryPredicate<Object>

public final class Constant<T>
extends Object
implements Function<T>, UnaryFunction<Object,T>, BinaryFunction<Object,Object,T>, Predicate, UnaryPredicate<Object>, BinaryPredicate<Object,Object>, Serializable

Evaluates to constant value.

Tests to a constant value, assuming a boolean of Boolean value is supplied. Note that although this class implements Serializable, a given instance will only be truly Serializable if the constant Object is. Attempts to serialize an instance whose value is not Serializable will result in an exception.

Version:

$Revision: 1160381 $ $Date: 2011-08-22 21:23:26 +0200 (Mon, 22 Aug 2011) $

Author:

Rodney Waldhoff

See Also:

Serialized Form

Field Summary

static Constant<Boolean>	FALSE Constant for false.
static Constant<Boolean>	TRUE Constant for true.

Constructor Summary

Constant(T value)
Create a new Constant.

Method Summary

boolean	equals(Constant<?> that) Learn whether another Constant is equal to this.
boolean	equals(Object that) Indicates whether some other object is "equal to" this functor.
T	evaluate() Evaluate this function.
T	evaluate(Object obj) Evaluate this function.
T	evaluate(Object left, Object right) Evaluate this function.
static Constant<Boolean>	falsePredicate() Get a Constant that always returns false.
int	hashCode() Returns a hash code for this functor adhering to the general Object.hashCode contract.
static <T> Constant<T>	of(T value) Get a Constant instance for the specified value.
static Constant<Boolean>	predicate(boolean value) Get a Constant that always returns value.
boolean	test() Evaluate this predicate.
boolean	test(Object obj) Evaluate this predicate.
boolean	test(Object left, Object right) Evaluate this predicate.
String	toString() Returns a human readable description of this functor.
static Constant<Boolean>	truePredicate() Get a Constant that always returns true.

Methods inherited from class java.lang.Object

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

Field Detail

TRUE

public static final Constant<Boolean> TRUE

Constant for true.

FALSE

public static final Constant<Boolean> FALSE

Constant for false.

Constructor Detail

Constant

public Constant(T value)

Create a new Constant.

Parameters:

value - Object

Method Detail

evaluate

public T evaluate()

Evaluate this function.

Specified by:

evaluate in interface Function<T>

Returns:

the T result of this evaluation

evaluate

public T evaluate(Object obj)

Evaluate this function.

Specified by:

evaluate in interface UnaryFunction<Object,T>

Parameters:

obj - the A object to evaluate

Returns:

the T result of this evaluation

evaluate

public T evaluate(Object left,
                  Object right)

Evaluate this function.

Specified by:

evaluate in interface BinaryFunction<Object,Object,T>

Parameters:

left - the L element of the ordered pair of arguments

right - the R element of the ordered pair of arguments

Returns:

the T result of this function for the given arguments

test

public boolean test()

Evaluate this predicate.

Specified by:

test in interface Predicate

Returns:

the result of this test

test

public boolean test(Object obj)

Evaluate this predicate.

Specified by:

test in interface UnaryPredicate<Object>

Parameters:

obj - the A object to test

Returns:

the result of this test

test

public boolean test(Object left,
                    Object right)

Evaluate this predicate.

Specified by:

test in interface BinaryPredicate<Object,Object>

Parameters:

left - the L element of the ordered pair of arguments

right - the R element of the ordered pair of arguments

Returns:

the result of this test for the given arguments

equals

public boolean equals(Object that)

Indicates whether some other object is "equal to" this functor. This method must adhere to general Object.equals contract. Additionally, this method can return true only if the specified Object implements the same functor interface and is known to produce the same results and/or side-effects for the same arguments (if any).

While implementators are strongly encouraged to override the default Object implementation of this method, note that the default Object implementation does in fact adhere to the functor equals contract.

Specified by:

equals in interface Functor

Overrides:

equals in class Object

Parameters:

that - the object to compare this functor to

Returns:

true iff the given object implements this functor interface, and is known to produce the same results and/or side-effects for the same arguments (if any).

See Also:

Functor.hashCode()

equals

public boolean equals(Constant<?> that)

Learn whether another Constant is equal to this.

Parameters:

that - Constant to test

Returns:

boolean

hashCode

public int hashCode()

Returns a hash code for this functor adhering to the general Object.hashCode contract. Implementators are strongly encouraged but not strictly required to override the default Object implementation of this method.

Specified by:

hashCode in interface Functor

Overrides:

hashCode in class Object

Returns:

a hash code for this functor

See Also:

Functor.equals(java.lang.Object)

toString

public String toString()

Returns a human readable description of this functor. Implementators are strongly encouraged but not strictly required to override the default Object implementation of this method.

Specified by:

toString in interface Functor

Overrides:

toString in class Object

Returns:

a human readable description of this functor

truePredicate

public static Constant<Boolean> truePredicate()

Get a Constant that always returns true.

Returns:

a Constant that always returns true

falsePredicate

public static Constant<Boolean> falsePredicate()

Get a Constant that always returns false.

Returns:

a Constant that always returns false

predicate

public static Constant<Boolean> predicate(boolean value)

Get a Constant that always returns value.

Parameters:

value - the constant value

Returns:

a Constant that always returns value

of

public static <T> Constant<T> of(T value)

Get a Constant instance for the specified value.

Type Parameters:

T - the constant value

Parameters:

value - T

Returns:

Constant