Java的消费者与回报[复制]

Question

这个问题已经在这里有一个答案：

• Why does a Java method reference with return type match the Consumer interface? 2个回答
• Why doesn't for-each method in java not throw an exception when a Function type argument is passed instead of Consumer? [duplicate] 3个回答

我不明白为什么这个代码工作：

class Resource {
    private Resource() {
        System.out.println("created...");
    }
    public Resource op1() {
        System.out.println("op1");
        return this;
    }
    public Resource op2() {
        System.out.println("op2");
        return this;
    }
    private void close() {
        System.out.println("clean up...");
    }
    public static void use(Consumer<Resource> block) {
        Resource resource = new Resource();
        try {
            block.accept(resource);
        }
        finally {
            resource.close();
        }
    }
}

// method call

public class App 
{
    public static void main( String[] args )
    {
      Consumer<Resource> block = resource -> resource.op1().op2(); //here
      Resource.use(block);
    }
}

消费者应该接受一个参数，并返回void。但是，在这个例子中消费者取一个参数（资源），并返回该参数。为什么它是工作，尽管我回到资源实例，而不是无效？

Answer 1

你Consumer<Resource> block = resource -> resource.op1().op2();相当于：

Consumer<Resource> block = new Consumer<Resource>() {
        @Override
        public void accept(Resource resource) {
            resource.op1().op2();  // there is no return statement
        }
    };