线程并发式放问单列懒汉模式的类

//线程并发式放问单列懒汉模式的类
//创建单例懒汉式类保证创建的对象唯一
class Single {
    private static void Single() {
    }

    private static Single s = null;

    public static Single getSingle() {
        //保证线程不会重复调用同步提高效率
        if (s == null) {
            synchronized (Demo.class) {
                if (s == null) {// 保证对象调用的唯一
                    s = new Single();
                }
            }
        }
        return s;
    }
}
    // 创建线程类
    class Demo implements Runnable {
        public void run() {
            Single s = Single.getSingle();
            System.out.println("s=" + s);
        }
    }

public class XianCheng {
    public static void main(String[] args) {
        Demo d = new Demo();
        Thread t = new Thread(d);
        Thread t2 = new Thread(d);
        t.start();
        t2.start();
    }
}