Java常用的单例模式

package com.mwq.singleton;
public class Singleton1 {
    private Singleton1() {
    }
    private static Singleton1 single = null;
    public static Singleton1 getInstance() {
        if (single == null) {
            return new Singleton1();
        }
        return single;
    }
    public String sayHello() {
        return "hello singleton1" + this;
    }
}

package com.mwq.singleton;
public class Singleton2 {
    private Singleton2() {
    }
    private static final Singleton2 single = new Singleton2();
    public static Singleton2 getInstance() {
        return single;
    }
    public String sayHello() {
        return "hello singleton2" + this;
    }
}

package com.mwq.singleton;
public enum Singleton3 {
    INSTANCE;
    public String sayHello() {
        return "hello singleton3" + this;
    }
}

package com.mwq.singleton;
public class Test extends Thread{
    public static void main(String[] args) {
        for (int i = 0; i < 10; i++) {
            new Thread(new Test()).start();
        }
    }
    @Override
    public void run() {
        System.out.println(Singleton1.getInstance().sayHello());
        System.out.println(Singleton2.getInstance().sayHello());
        System.out.println(Singleton3.INSTANCE.sayHello());
        System.out.println();
    }
}

hello singleton1com.mwq.singleton.Singleton1@1b1aa65
hello singleton2com.mwq.singleton.Singleton2@1125127
hello singleton3INSTANCE
hello singleton1com.mwq.singleton.Singleton1@bb7465
hello singleton1com.mwq.singleton.Singleton1@2a5330
hello singleton2com.mwq.singleton.Singleton2@1125127
hello singleton3INSTANCE
hello singleton2com.mwq.singleton.Singleton2@1125127
hello singleton3INSTANCE