设计模式之单例模式

单例模式

package com.hml.singleton;

/**
* 饿汉式
*/
public class Singleton {
private static Singleton instance  = new Singleton();

private Singleton(){}
public static Singleton getInstance () {
return instance;
}
}

package com.hml.singleton;

/**
* 懒汉式
*/
public class Singleton2 {

private static Singleton2 instance;
private Singleton2() {}
public static Singleton2 getInstance() {
if (instance == null) {
instance = new Singleton2();
}
return instance;
}
}

package com.hml.singleton;

/**
* 双重锁定
*/
public class Singleton3 {

private static Singleton3 instance;

private Singleton3(){}

public static Singleton3 getInstance() {
if (instance == null) {
synchronized (Singleton3.class) {
if (instance == null) {
instance = new Singleton3();
}
}
}
return instance;
}
}