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

      All Methods Static Methods Instance Methods Abstract Methods Default Methods 
      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 Detail

      • 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