设计模式之单例模式

1. 懒汉式

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

1. 饿汉式

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

懒汉式和饿汉式的区别：
饿汉式：类一旦加载，就把单例初始化完成
懒汉式：只有调用getInstance的时候才去初始化这个单例