Double-Checked-Locking模式

package com.ymjin.doubleMoshi;/** * 这就是Double-Checked-Locking模式 * - * @author xiaoyu * */public class USTax {private static USTax instance = null;private USTax() {}private synchronized static void doSync() {if (instance == null) {System.out.println("实例不存在");instance = new USTax();System.out.println("实例创建成功");} else {System.out.println("实例已经被创建");}}@SuppressWarnings("unused")private static USTax getInstance() {if (instance == null) {System.out.println("实例不存在");doSync();} else {System.out.println("实例已经存在");}return instance;}}