[singleton单子模式]
单子模式1:

public class Singleton {//1.私有的静态类变量;//2.私有的构造子;//3.公有的静态工厂方法private static Singleton instance = null;private Singleton(){}synchronized public static Singleton getInstance() {if (instance == null)instance = new Singleton();return instance;}}

public class Singleton {/* 1.私有的静态类变量; 2.构造子私有; 3.公有的静态工厂方法; */private static Singleton instance = new Singleton();private Singleton() {}public static Singleton getInstance() {return instance;}}