创建型（单例模式）
package com.lwf.create.singleton;public class Singleton {private Singleton(){}private static Singleton st = new Singleton();public static Singleton getInstance(){return st;}public static void main(String[] args) {}}class LazySingleton{private LazySingleton(){}private static LazySingleton st = null;public static synchronized LazySingleton getInstance(){if(st == null)st = new LazySingleton();return st;}}class Test{public static void main(String[] args) {Singleton st = Singleton.getInstance();LazySingleton lzSt = LazySingleton.getInstance();}}?