单例模式DCL（double check lock）

package com.cy.SingtonInstance;


import sun.security.jca.GetInstance;

public class DCLSingletonInstanceDemo {
    private static volatile DCLSingletonInstanceDemo instance = null;

    private DCLSingletonInstanceDemo() {
        System.out.println("constructor method....");
    }

    //DCL(double check lock机制)
    public static DCLSingletonInstanceDemo getInstance() {
        if (instance == null) {
            synchronized (DCLSingletonInstanceDemo.class) {
                if (instance == null) {
                    instance = new DCLSingletonInstanceDemo();
                }
            }
        }
        return instance;
    }

    public static void main(String[] args) {

        for (int i = 1; i <= 10; i++) {
            new Thread(() -> {
                DCLSingletonInstanceDemo.getInstance();
            }, String.valueOf(i)).start();
        }
    }
}