单例模式

package com.kevin;

// 懒汉模式 调用静态方法的时候实例化
public class Singleton1 {
    private String name = "lazy";

    private Singleton1() {
    }

    private static Singleton1 single = null;

    //静态工厂方法
    public static Singleton1 getInstance() {
        if (single == null) {
            single = new Singleton1();
        }
        return single;
    }

    // 线程安全
    /*public static synchronized Singleton getInstance() {
        if (single == null) {
            single = new Singleton();
        }
        return single;
    }*/

    // 双重检查锁定
    /*public static Singleton getInstance() {
        if (singleton == null) {
            synchronized (Singleton.class) {
                if (singleton == null) {
                    singleton = new Singleton();
                }
            }
        }
        return singleton;
    }*/

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void printInfo() {
        System.out.println("the name is " + name);
    }
}

package com.kevin;

// 饿汉模式 类加载的时候实例化
public class Singleton2 {
    private Singleton2() {
    }

    private static final Singleton2 single = new Singleton2();

    //静态工厂方法
    public static Singleton2 getInstance() {
        return single;
    }
}

package com.kevin;

import java.io.Serializable;

// test singleton function
// 饿汉式天生就是线程安全的，可以直接用于多线程而不会出现问题，
// 懒汉式本身是非线程安全的
// 单例模式特点
// 只有一个实例存在

public class MainTest implements Serializable {

public static void main(String[] args) {
        test2();
    }

    private static void test1() {
        Singleton1 s1 = Singleton1.getInstance();
        s1.setName("22222");
        s1.printInfo();;
        Singleton1 s2 = Singleton1.getInstance();
        // 输出name的值，是s1的name的值
        s2.printInfo();
        s2.setName("33333");
        // 设置s2的name的值，s1的name值已经变化
        s1.printInfo();
    }

    private static void test2() {
        Singleton1 s1 = Singleton1.getInstance();
        s1.setName("aaaa");
        Singleton1 s2 = Singleton1.getInstance();
        s2.setName("bbbbb");
        System.out.println(s1 == s2);
    }
}