单例模式

public class Singleton {
    //单例设计模式，禁止指令重排可以加volatile
    private static Singleton singleton = null;

    private void Singleton() {
        System.out.println(Thread.currentThread().getName() + "构造方法执行");
    }
    //DCL（Double Check lock双端检索机制）
    public static Singleton getInstance() {
        if (singleton == null) {
            synchronized (Singleton.class) {
                if (singleton == null) {
                    singleton=new Singleton();
                }
            }
        }
        return singleton;
    }
}