Module java.base
Package java.util.function

Interface Function<T,​R>

Type Parameters:
T - the type of the input to the function
R - the type of the result of the function
All Known Subinterfaces:
UnaryOperator<T>
Functional Interface:
This is a functional interface and can therefore be used as the assignment target for a lambda expression or method reference.
@FunctionalInterface public interface Function<T,​R>
Represents a function that accepts one argument and produces a result.

This is a functional interface whose functional method is apply(Object).

Since:
1.8

  • Method Summary

    Modifier and Type
    Method
    Description
    default <V> Function<T,​V>
    andThen​(Function<? super R,​? extends V> after)
    Returns a composed function that first applies this function to its input, and then applies the after function to the result.
    R
    apply​(T t)
    Applies this function to the given argument.
    default <V> Function<V,​R>
    compose​(Function<? super V,​? extends T> before)
    Returns a composed function that first applies the before function to its input, and then applies this function to the result.
    static <T> Function<T,​T>
    identity()
    Returns a function that always returns its input argument.

  • Method Details

    • apply

      R apply​(T t)
      Applies this function to the given argument.
      Parameters:
      t - the function argument
      Returns:
      the function result

    • compose

      default <V> Function<V,​R> compose​(Function<? super V,​? extends T> before)
      Returns a composed function that first applies the before function to its input, and then applies this function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function.
      Type Parameters:
      V - the type of input to the before function, and to the composed function
      Parameters:
      before - the function to apply before this function is applied
      Returns:
      a composed function that first applies the before function and then applies this function
      Throws:
      NullPointerException - if before is null
      See Also:
      andThen(Function)

    • andThen

      default <V> Function<T,​V> andThen​(Function<? super R,​? extends V> after)
      Returns a composed function that first applies this function to its input, and then applies the after function to the result. If evaluation of either function throws an exception, it is relayed to the caller of the composed function.
      Type Parameters:
      V - the type of output of the after function, and of the composed function
      Parameters:
      after - the function to apply after this function is applied
      Returns:
      a composed function that first applies this function and then applies the after function
      Throws:
      NullPointerException - if after is null
      See Also:
      compose(Function)

    • identity

      static <T> Function<T,​T> identity()
      Returns a function that always returns its input argument.
      Type Parameters:
      T - the type of the input and output objects to the function
      Returns:
      a function that always returns its input argument