线程（四）

一、单例模式

1、双重检查

public class SingletonClass {

    private void SingletonClass(){}

    private static SingletonClass singletonClass = null;

    public static SingletonClass getInstance() {
        if (singletonClass == null) {
//            try {
//                Thread.sleep(1000 * 2);
//            } catch (InterruptedException e) {
//                e.printStackTrace();
//            }
            synchronized (SingletonClass.class) {
                if (singletonClass == null) {
                    return singletonClass = new SingletonClass();
                }
            }
        }
        return singletonClass;
    }

    public static void main(String[] args) {
        new Thread(new Runnable() {
            public void run() {
                System.out.println(SingletonClass.getInstance().hashCode());
            }
        }).start();

        new Thread(new Runnable() {
            public void run() {
                System.out.println(SingletonClass.getInstance().hashCode());
            }
        }).start();

        new Thread(new Runnable() {
            public void run() {
                System.out.println(SingletonClass.getInstance().hashCode());
            }
        }).start();
    }
}

双重if判断

 

转载于:https://my.oschina.net/u/2504766/blog/758517