第二章 单例模式练习.ppt

计算机科学与工程学院 UML与设计模式 No.*/10 第1章 OO方法概述 第二章 单例模式练习 2014年3月 Singleton设计模式 练习：使用Singleton模式，编写并测试GenerateID类，生成唯一ID值 private long currentID=1000; public long getID() Singleton代码示例 public class GenerateID { private static GenerateID singleton = new GenerateID(); private GenerateID(){} public static GenerateID getInstance(){ return singleton; } private long currentID=1000; public long getID(){ return currentID++; } } class TestID { public static void main(String args[]){ GenerateID g1=GenerateID.getInstance(); GenerateID g2=GenerateID.getInstance(); System.out.println(g1.getID()); System.out.println(g2.getID()); System.out.println(g1.getID()); System.out.println(g2.getID()); } } Singleton代码示例 public class GenerateID { private static GenerateID singleton ; private GenerateID(){} public synchronized static GenerateID getInstance(){ if (singleton == null) { singleton = = new GenerateID(); } return singleton; } private long currentID=1000; public long getID(){ return currentID++; } } class TestID { public static void main(String args[]){ GenerateID g1 = GenerateID.getInstance(); GenerateID g2 = GenerateID.getInstance(); System.out.println(g1.getID()); System.out.println(g2.getID()); System.out.println(g1.getID()); System.out.println(g2.getID()); } } Singleton设计模式 作业：编写TrafficLight类，使其只有红，黄，绿三个实例(使用HashMap) HashMap键值对应（key,value），一个key对应一个值。知道key就可以取到对应的值。 Map map = new HashMap(); map.put(xxx,new TrafficLight(xxx)); map.put(yyy,new TrafficLight(yyy)); Object o=map.get(xxx); TrafficLight t=(TrafficLight).get(xxx); import java.util.*; public class TrafficLight { private String color ; private static Map map = new HashMap(); private TrafficLight(String color){ this.color = color; } public synchronized static TrafficLight getLight(String color){ if (map.size()==0) { map.put(red, new TrafficLight(red)); map.put(yellow, new TrafficLight(yellow)); map.put(green, new TrafficLight(green