@GwtCompatible @CheckReturnValue public final class Functions extends Object
Static utility methods pertaining to Function instances.
All methods return serializable functions as long as they’re given serializable parameters.
See the Guava User Guide article on the use of Function.
| Modifier and Type | Method and Description |
|---|---|
static <A,B,C> Function<A,C> |
compose(Function<B,C> g,
Function<A,? extends B> f)
Returns the composition of two functions.
|
static <E> Function<Object,E> |
constant(E value)
Creates a function that returns
value for any input. |
static <K,V> Function<K,V> |
forMap(Map<K,? extends V> map,
V defaultValue)
Returns a function which performs a map lookup with a default value.
|
static <K,V> Function<K,V> |
forMap(Map<K,V> map)
Returns a function which performs a map lookup.
|
static <T> Function<T,Boolean> |
forPredicate(Predicate<T> predicate)
Creates a function that returns the same boolean output as the given predicate for all inputs.
|
static <T> Function<Object,T> |
forSupplier(Supplier<T> supplier)
Returns a function that always returns the result of invoking
Supplier.get() on supplier, regardless of its input. |
static <E> Function<E,E> |
identity()
Returns the identity function.
|
static Function<Object,String> |
toStringFunction()
Returns a function that calls
toString() on its argument. |
public static Function<Object,String> toStringFunction()
Returns a function that calls toString() on its argument. The function does not accept nulls; it will throw a NullPointerException when applied to null.
Warning: The returned function may not be consistent with equals (as documented at Function.apply(T)). For example, this function yields different results for the two equal instances ImmutableSet.of(1, 2) and ImmutableSet.of(2, 1).
public static <E> Function<E,E> identity()
Returns the identity function.
public static <K,V> Function<K,V> forMap(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.
Note: if map is a BiMap (or can be one), you can use Maps.asConverter instead to get a function that also supports reverse conversion.
public static <K,V> Function<K,V> forMap(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.
map - source map that determines the function behaviordefaultValue - the value to return for inputs that aren’t map keysmap.get(a) when a is a key, or defaultValue otherwisepublic static <A,B,C> Function<A,C> compose(Function<B,C> g, 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.
g - the second function to applyf - the first function to applyf and gpublic static <T> Function<T,Boolean> forPredicate(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.
public static <E> Function<Object,E> constant(@Nullable E value)
Creates a function that returns value for any input.
value - the constant value for the function to returnvalue@Beta public static <T> Function<Object,T> forSupplier(Supplier<T> supplier)
Returns a function that always returns the result of invoking Supplier.get() on supplier, regardless of its input.