Java 8 lambda Void参数 [英] Java 8 lambda Void argument

问题描述

假设我在Java 8中有以下功能接口：

Let's say I have the following functional interface in Java 8:

interface Action<T, U> {
   U execute(T t);
}

在某些情况下，我需要一个没有参数或返回类型的操作。所以我写这样的
：

And for some cases I need an action without arguments or return type. So I write something like this:

Action<Void, Void> a = () -> { System.out.println("Do nothing!"); };

然而，它给我编译错误，我需要把它写成

However, it gives me compile error, I need to write it as

Action<Void, Void> a = (Void v) -> { System.out.println("Do nothing!"); return null;};

哪个很难看。有没有办法摆脱 Void 类型参数？

Which is ugly. Is there any way to get rid of the Void type parameter?

推荐答案

你后的语法是可能的，其将一个可运行一个小的辅助功能到动作<空隙，空隙率> （例如，您可以将其放在行动）：

The syntax you're after is possible with a little helper function that converts a Runnable into Action<Void, Void> (you can place it in Action for example):

public static Action<Void, Void> action(Runnable runnable) {
    return (v) -> {
        runnable.run();
        return null;
    };
}

// Somewhere else in your code
 Action<Void, Void> action = action(() -> System.out.println("foo"));

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