Method Detail

• toStringFunction

  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(F)). For example, this function yields different results for the two equal instances ImmutableSet.of(1, 2) and ImmutableSet.of(2, 1).

• identity

  public static <E> Function<E,E> identity()

  Returns the identity function.

• forMap

  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.

• forMap

  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.

  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> 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.

  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> 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(F)) if and only if predicate is itself consistent with equals.

• constant

  public static <E> Function<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

  @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.

  Since:

  10.0