程序包 java.util.function

接口 Function<T,R>

类型参数:

T - the type of the input to the function

R - the type of the result of the function

所有已知子接口:

UnaryOperator<T>

函数接口:

这是一个函数接口, 因此可用作 lambda 表达式或方法引用的赋值目标。

@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(java.lang.Object).

从以下版本开始:

1.8

方法概要

限定符和类型	方法	说明
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.

方法详细资料

apply

R apply(T t)

Applies this function to the given argument.

参数:

t - the function argument

返回:

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.

类型参数:

V - the type of input to the before function, and to the composed function

参数:

before - the function to apply before this function is applied

返回:

a composed function that first applies the before function and then applies this function

抛出:

NullPointerException - if before is null

另请参阅:

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.

类型参数:

V - the type of output of the after function, and of the composed function

参数:

after - the function to apply after this function is applied

返回:

a composed function that first applies this function and then applies the after function

抛出:

NullPointerException - if after is null

另请参阅:

compose(Function)

identity

static <T> Function<T,T> identity()

Returns a function that always returns its input argument.

类型参数:

T - the type of the input and output objects to the function

返回:

a function that always returns its input argument