2020.02.16 懒汉式单例模式

package com.guoyun.ThreadTest;

/**
 * ClassName:
 * Function:  ADD FUNCTION
 * Reason:   ADD REASON
 *
 * @author
 * @Date
 * @since Ver 1.1
 */
public class InstanceDemo {
    private static InstanceDemo instance=null;
    private  InstanceDemo(){}
    public static InstanceDemo getInstance(){
        if (instance==null){
            synchronized (InstanceDemo.class){
                if (instance==null){
                    instance=new InstanceDemo();
                }
            }
        }
        return instance;

    }
}