com.diffplug.common.base

Class Functions

java.lang.Object

com.diffplug.common.base.Functions

public final class Functions
extends java.lang.Object

The APIs below are identical to Google's Guava 18.0, except that guava's functional interfaces have been swapped with Java 8's. It is tested against the same test suite as Google Guava to ensure functional compatibility. Most of the implementation has been replaced with lambdas, which means that the following functionality has been removed: equals(), hashCode(), toString(), GWT, and serialization. Lambdas don't support these methods, and there isn't much reason why they should, so we removed them in Durian.

Method Summary

Modifier and Type	Method and Description
static <A,B,C> java.util.function.Function<A,C>	compose(java.util.function.Function<B,C> g, java.util.function.Function<A,? extends B> f) Returns the composition of two functions.
static <E> java.util.function.Function<java.lang.Object,E>	constant(E value) Creates a function that returns value for any input.
static <K,V> java.util.function.Function<K,V>	forMap(java.util.Map<K,? extends V> map, V defaultValue) Returns a function which performs a map lookup with a default value.
static <K,V> java.util.function.Function<K,V>	forMap(java.util.Map<K,V> map) Returns a function which performs a map lookup.
static <T> java.util.function.Function<T,java.lang.Boolean>	forPredicate(java.util.function.Predicate<T> predicate) Creates a function that returns the same boolean output as the given predicate for all inputs.
static <T> java.util.function.Function<java.lang.Object,T>	forSupplier(java.util.function.Supplier<T> supplier) Returns a function that always returns the result of invoking Supplier.get() on supplier, regardless of its input.
static <E> java.util.function.Function<E,E>	identity() Returns the identity function.

Methods inherited from class java.lang.Object

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

Method Detail

identity

public static <E> java.util.function.Function<E,E> identity()

Returns the identity function.

forMap

public static <K,V> java.util.function.Function<K,V> forMap(java.util.Map<K,V> map)

Returns a function which performs a map lookup. The returned function throws an IllegalArgumentException if given a key that does not exist in the map. See also forMap(Map, Object), which returns a default value in this case.

forMap

public static <K,V> java.util.function.Function<K,V> forMap(java.util.Map<K,? extends V> map,
                                                            @Nullable
                                                            V defaultValue)

Returns a function which performs a map lookup with a default value. The function created by this method returns defaultValue for all inputs that do not belong to the map's key set. See also forMap(Map), which throws an exception in this case.

Parameters:

map - source map that determines the function behavior

defaultValue - the value to return for inputs that aren't map keys

Returns:

function that returns map.get(a) when a is a key, or defaultValue otherwise

compose

public static <A,B,C> java.util.function.Function<A,C> compose(java.util.function.Function<B,C> g,
                                                               java.util.function.Function<A,? extends B> f)

Returns the composition of two functions. For f: A->B and g: B->C, composition is defined as the function h such that h(a) == g(f(a)) for each a.

Parameters:

g - the second function to apply

f - the first function to apply

Returns:

the composition of f and g

See Also:

function composition

forPredicate

public static <T> java.util.function.Function<T,java.lang.Boolean> forPredicate(java.util.function.Predicate<T> predicate)

Creates a function that returns the same boolean output as the given predicate for all inputs.

The returned function is consistent with equals (as documented at Function.apply(T)) if and only if predicate is itself consistent with equals.

constant

public static <E> java.util.function.Function<java.lang.Object,E> constant(@Nullable
                                                                           E value)

Creates a function that returns value for any input.

Parameters:

value - the constant value for the function to return

Returns:

a function that always returns value

forSupplier

public static <T> java.util.function.Function<java.lang.Object,T> forSupplier(java.util.function.Supplier<T> supplier)

Returns a function that always returns the result of invoking Supplier.get() on supplier, regardless of its input.

Since:

10.0