下面的代码怎么修改，才能保证线程里不报空指针异常

Question

public class Test {
private String key;

private Thread myThread = new Thread() {
    public void run() {
        String threadKey = key.replace(" ", "").replace("-", "");
        System.out.println(threadKey);
    };
};

public void doTask() {
    key = "aa";
    myThread.start();
    key = null;
}

public static void main(String[] args) {
    Test test = new Test();
    test.doTask();
}

}

Answer 1

提供两种方法 一种利用Thread join，另一种使用线程同步锁 实测可行 有详细注释 望采纳

 public class Test {

    private String key;

    private Thread myThread = new Thread() {
        public void run() {
            String threadKey = key.replace(" ", "").replace("-", "");
            System.out.println(threadKey);
        }
    };

    public void doTask() {
        key = "aa";
        myThread.start();

        // Thread join 可使得多线程间并行执行变为串行执行
        // myThread join 到主线程 必须等 myThread 执行完 主线程才能继续
        try {
            myThread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        key = null;
    }

    public static void main(String[] args) {
        Test test = new Test();
        test.doTask();
    }
}

public class Test {

    private String key;

    private Thread myThread = new Thread() {
        public void run() {
            String threadKey = key.replace(" ", "").replace("-", "");
            System.out.println(threadKey);

            // myThread 执行完毕 释放主线程锁
            synchronized (Test.this) {
                Test.this.notifyAll();
            }
        }
    };

    public void doTask() {
        key = "aa";
        myThread.start();

        // 把主线程锁起来
        synchronized (this) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        key = null;
    }

    public static void main(String[] args) {
        Test test = new Test();
        test.doTask();
    }
}