单例模式的4种写法

1、饿汉式

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

2、懒汉式

//加同步，确保线程安全

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

 

3、静态内部类

public class Singleton {private static class single{private static final Singleton instance = new Singleton();}public static final Singleton getInstance(){return single.instance;}}

4、枚举

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