设计模式之单例、多例模式

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单例设计模式只提供一个全局对象

饿汉式

public class NormalSingleton {

   private static NormalSingleton s = new NormalSingleton();
   private NormalSingleton(){}
   public static NormalSingleton getInstance(){
       return s;
   }

}

懒汉式

public class LazySingleton {
   private static LazySingleton s = null;
   private LazySingleton(){}
   public static synchronized LazySingleton getInstance(){
       if(s==null){
           s = new LazySingleton();
       }
       return s;
   }
}

多例模式

public class Multileton {
   private static final int N = 10;
   private static List<Multileton> l = new ArrayList<Multileton>(N);
   //对象的序号
   private int no;
   private Multileton(int no){
       this.no = no;
       System.out.println("Create ["+ no +"] instance");
   }
   static{
       for(int i = 0; i<N;i++ ){
           l.add(new Multileton(i));
       }
   }

   public static Multileton getRondomInstance(){
       int num = (int)(Math.random()*N);
       return l.get(num);
   }

   public int getNo() {
       return no;
   }

   public void setNo(int no) {
       this.no = no;
   }

}

测试

public class MainApp {
   public static void main(String[] args) {
//       NormalSingleton s1 = NormalSingleton.getInstance();
//       NormalSingleton s2 = NormalSingleton.getInstance();
//       System.out.println(s1==s2);

//       LazySingleton s1 = LazySingleton.getInstance();
//       LazySingleton s2 = LazySingleton.getInstance();
//       System.out.println(s1==s2);

       Multileton ml1 = Multileton.getRondomInstance();
       Multileton ml2 = Multileton.getRondomInstance();
       System.out.println(ml1==ml2);

   }

}

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