23种设计模式-单例模式

package com.nuoyuan.preone.utils;


/**
 * Author: yangweichao
 * Date:   2019/2/21 4:04 PM
 * Description: 一个进程中只存在唯一一个对象
 */


// 饿汉式
public class SingleTon {


    private static SingleTon singleTon = new SingleTon();

    private SingleTon() {
    }

    public static SingleTon getInstance() {

        return singleTon;
    }
}


/**
 *
 * 懒汉式的特点是延迟加载，比如配置文件，采用懒汉式的方法，顾名思义，懒汉么，很懒的，配置文件的实例直到用到的
 * 时候才会加载。。。。。。
 *
 * 懒汉式
 */

public class SingleTon {


    private static SingleTon singleTon = null;

    private SingleTon() {
    }

    public static SingleTon getInstance() {
        if (singleTon == null) {
            singleTon = new SingleTon();
        }
        return singleTon;
    }
}


//带锁方式 兼容并发
public class SingleTon {


    private static SingleTon singleTon = null;

    private SingleTon() {
    }

    public static SingleTon getInstance() {
        if (singleTon == null) {
            synchronized (SingleTon.class) {
                if (singleTon == null)
                    singleTon = new SingleTon();
            }
        }
        return singleTon;
    }
}