2

在下面的代码中，我想知道为什么内联类中的 run() 能够访问外部类变量 - 信号量（即使它没有声明为 final）。

    private Semaphore semaphore = new Semaphore(bufferSize);

    private Runnable producerRunnable = new Runnable(){

        @Override
        public void run()
        {
            try
            {
                semaphore.acquire();
            }
            catch(InterruptedException e)
            {
                System.out.println("producer was interrupted while trying to acquire semaphore");                   
            }
        }
   };

我希望 Eclipse 标记编译错误 - 因为信号量引用未声明为 final

4

2 回答 2

2

这个是正常的。最终要求仅描述为适用于局部变量和参数 ( JLS )：

任何使用但未在内部类中声明的局部变量、形式参数或异常参数都必须声明为 final [...]。

封闭实例的成员不需要是 final 来访问它们。

于 2014-03-21T03:31:54.407 回答
0

因为您已将信号量定义为该类的全局变量，并且如果您想在 runnable 中访问它，所有局部变量都应声明为 final。

public class KamalTest {

    /**
     * @param args the command line arguments
     */
    private Semaphore semaphore = new Semaphore(2);
    private Runnable producerRunnable = new Runnable() {
        @Override
        public void run() {
            try {
                semaphore.acquire();
            } catch (InterruptedException e) {
                System.out.println("producer was interrupted while trying to acquire semaphore");
            }
        }
    };

    public void startThread1() {
        Thread th = new Thread(producerRunnable);
        th.start();
    }

    public void startThread2() {
        final Semaphore semPhore = new Semaphore(2);

        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                try {
                    semPhore.acquire();
                } catch (InterruptedException ex) {
                    Logger.getLogger(KamalTest.class.getName()).log(Level.SEVERE, null, ex);
                }
            }
        };


        Thread th = new Thread(runnable);
        th.start();
    }

    public static void main(String[] args) {

        KamalTest kt = new KamalTest();
        kt.startThread1();


        System.out.println("Internet Available : " + isInternetAvailable());

    }
}


}
于 2014-03-21T03:46:55.427 回答