当SAM方法未在Java中返回值时，Lambda会返回一个值 [英] Lambda works to return a value when SAM method doesnt return a value in java

问题描述

@FunctionalInterface
public interface Runnable {
    public abstract void run();
}

public class MethodReference1 {

    public static String ThreadStatus() {
        System.out.println( Thread.currentThread().getName() +  " is running...");
        return "threadname";
    }

    public static void main(String[] args) {
        Thread t1 = new Thread(() -> ThreadStatus());
        t1.start();
    }

}

在上述使用Java 8的示例中，ThreadStatus()返回一个字符串，但Runnable接口"run()"方法未返回任何值.但它仍然有效(无编译/运行时错误).我想知道它是如何工作的，因为根据lamba规范，SAM应该具有完全相同的签名.

In the above example using Java 8, ThreadStatus() returns a string but Runnable interface "run()" method doesnt return any value. But it still works (No compile/runtime error). I am wondering how it is working because as per the lamba specification, SAM should have exactly same signature.

如果我翻转了ThreadStatus方法不返回任何值的情况，并更改了Functional接口方法以返回值，则会出现编译时错误.

If i flip the case where ThreadStatus method doesnt return any value and change the Functional interface method to return a value, i get a compile time error.

有人可以帮助我理解这一点吗?

Can someone help me understand this?

推荐答案

这是因为Thread t1 = new Thread(() -> ThreadStatus());等效于:

Thread t1 = new Thread(new Runnable() {
    @Override
    public void run() {
        ThreadStatus();
    }
});

因此您不会从run()返回任何内容.只需指示run()调用ThreadStatus()方法并忽略返回值即可.

So you're not returning anything from run(). run() is simply instructed to invoke the ThreadStatus() method and ignore the return value.

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