Java8方法引用用作Function对象来组合函数 [英] Java8 method reference used as Function object to combine functions
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问题描述
Java8中是否有办法使用方法引用作为 Function
对象来使用其方法,如:
Is there a way in Java8 to use a method reference as a Function
object to use its methods, something like:
Stream.of("ciao", "hola", "hello")
.map(String::length.andThen(n -> n * 2))
此问题与 Stream $ c $无关c>,它只是用作例子,我想对方法参考有答案
This question is not related to the Stream
, it is used just as example, I would like to have answer about the method reference
推荐答案
你可以写一个静态的执行此操作的方法:
You can write a static method to do this:
import java.util.function.*;
class Test {
public static void main(String[] args) {
Function<String, Integer> function = combine(String::length, n -> n * 2);
System.out.println(function.apply("foo"));
}
public static <T1, T2, T3> Function<T1, T3> combine(
Function<T1, T2> first,
Function<T2, T3> second) {
return first.andThen(second);
}
}
然后你可以将它放在一个实用程序类中并导入静态地。
You could then put it in a utility class and import it statically.
或者,创建一个更简单的静态方法,只是返回它给出的函数,为了让编译器知道你的'重做:
Alternatively, create a simpler static method which just returns the function it's given, for the sake of the compiler knowing what you're doing:
import java.util.function.*;
class Test {
public static void main(String[] args) {
Function<String, Integer> function = asFunction(String::length).andThen(n -> n * 2);
System.out.println(function.apply("foo"));
}
public static <T1, T2> Function<T1, T2> asFunction(Function<T1, T2> function) {
return function;
}
}
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