Java 8 Lambda 表达式不起作用

Question

我正在尝试以下代码并使用 JDK 1.8.0_66 进行编译。我的代码在语法上似乎是正确的，我错过了什么吗？

interface Executable {
    void execute();
}

class Runner {
    public void run(Executable e) {
        System.out.println("Executing code block!");
        e.execute();
    }
}

public class HelloWorld {
    public static void main(String[] args) {
        Runner runner = new Runner();

        runner.run(new Executable() {
            public void execute() {
                System.out.println("IN ANONYMOUS CLASS EXECUTE");
            }
        });
    }

    runner.run(() -> System.out.println());

}

抛出以下编译错误:

App.java:25: error: <identifier> expected
        runner.run(() -> System.out.println());
                  ^
App.java:25: error: illegal start of type
        runner.run(() -> System.out.println());
                   ^
App.java:25: error: ';' expected
        runner.run(() -> System.out.println());

Answer 1

您的语句位于定义 runnner 变量的 block 之外。应该是这样的:

public static void main(String[] args) {
    Runner runner = new Runner();

    runner.run(new Executable() {
        public void execute() {
            System.out.println("IN ANONYMOUS CLASS EXECUTE");
        }
    });

    runner.run(() -> System.out.println());
}