设计模式-单例模式实现过程案例

设计思路：1.创建静态私有对象；2.构造方法私有化；3.静态公有的对象地址方法

一.

/**
 * @author jiagx
 * @description 单例模式-线程不安全版本
 * @date 2020/5/27 9:54
 */
public class Singleton {

    private static Singleton singleton;

    private  Singleton(){
    };

    public static Singleton getInstance(){
        if (singleton==null){
            singleton=new Singleton();
        }
        return singleton;
    }

}


二.

/**
 * @author jiagx
 * @description 单例模式-同步锁单例模式
 * @date 2020/5/27 9:58
 */
public class SingletonSyn {
    private static SingletonSyn singleton;

    private SingletonSyn(){};

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


三.

/**
 * @author jiagx
 * @description 单例模式-双层校验锁机制的同步锁单例模式
 * @date 2020/5/27 10:12
 */
public class SingletonSyn2 {

    private static SingletonSyn2 singletonSyn2;

    private SingletonSyn2(){

    }


    public static synchronized SingletonSyn2 getInstance(){

        if (singletonSyn2==null){
            synchronized (SingletonSyn2.class){
                if (singletonSyn2==null){
                    singletonSyn2=new SingletonSyn2();
                }
            }
        }
        return singletonSyn2;
    }
}


四.

/**
 * @author jiagx
 * @description 单例模式-无锁线程安全单例模式,最优秀的单例模式
 * @date 2020/5/27 10:38
 */
public class SingletonSynNoLock {

    private final static SingletonSynNoLock singletonSynNoLock = new SingletonSynNoLock();

    private SingletonSynNoLock(){};

    @Synchronized
    public static  SingletonSynNoLock getInstance(){
        return singletonSynNoLock;
    }

}