单例模式学习及控制实例化对象个数

单例模式学习：

package com.amaker.single;

import java.util.HashMap;
import java.util.Map;

public class People {
	//===============================================================
	//标准的单例
	private static People p = null;
	private People(){
		
	}
	
	public static People getInstance(){
		if(p==null){
			p = new People();
		}
		return p;
	}
	//===============================================================
	//利用缓存的单例
	private static Map<String,People> map = new HashMap<String,People>();
	public static People getInstance2(){
		People p = map.get("one");
		if(p==null){
			p = new People();
			map.put("one", p);
		}
		return p;
	}
	//===============================================================
	//实例化三个或更多实例，可以按要求实例化对象个数,如下面的count可以从配置文件中读取
	private static int number = 1;
	private static int count = 3;
	public static People getInstance3(){
		p = map.get(number+"");
		if(p==null){
			p = new People();
			map.put(number+"", p);
		}
		number++;
		if(number>count){
			number = 1;
		}
		return p;
	}
}

package com.amaker.client;

import com.amaker.single.People;

public class Test {
	public static void main(String[] args) {
		//单例测试：
		/*People p1 = People.getInstance();
		System.out.println("p=="+p1);
		
		People p2 = People.getInstance();
		System.out.println("p=="+p2);
		
		People p3 = People.getInstance();
		System.out.println("p=="+p3);
		*/
		
		//缓存测试：
		/*People p1 = People.getInstance2();
		System.out.println("p=="+p1);
		
		People p2 = People.getInstance2();
		System.out.println("p=="+p2);
		
		People p3 = People.getInstance2();
		System.out.println("p=="+p3);*/
		
		//控制对象的个数,暂时实例化三个对象
		People p1 = People.getInstance3();
		System.out.println("p=="+p1);
		
		People p2 = People.getInstance3();
		System.out.println("p=="+p2);
		
		People p3 = People.getInstance3();
		System.out.println("p=="+p3);
		
		People p4 = People.getInstance3();
		System.out.println("p=="+p4);
		
		People p5 = People.getInstance3();
		System.out.println("p=="+p5);
		
	}
}