单例模式之多例类【设计模式】
单例模式:单例模式
多例类:请使用单例模式编写一个程序,然后考虑一下如何对这个程序进行改造,使得系统中某个类的对象可以存在有限多个,例如两例或三例?
法一:最多有max_num种实例,如果调用次数超过,则默认为第max_num种
代码如下:
public class KFC {
private static ArrayList<TaoCan> taocan = new ArrayList<TaoCan>();
static int num = 0;
static int max_num = 3;
public static TaoCan getinstance(){//最多有max_num种套餐,如果调用次数超过,则默认为最后一种
synchronized (KFC.class) {
if(num < max_num){
num++;
taocan.add(new TaoCan());
}
}
return taocan.get(num-1);
}
}
测试类:
package KFC;
public class Customer {
public static void main(String[] args) {
KFC kfc = new KFC();
TaoCan customer1 = kfc.getinstance();
TaoCan customer2 = kfc.getinstance();
TaoCan customer3 = kfc.getinstance();
TaoCan customer4 = kfc.getinstance();
TaoCan customer5 = kfc.getinstance();
System.out.println("customer1 == customer2? " + customer1.equals(customer2));
System.out.println("customer1 == customer3? " + customer1.equals(customer3));
System.out.println("customer2 == customer3? " + customer2.equals(customer3));
System.out.println("customer3 == customer5? " + customer3.equals(customer5));
System.out.println("customer4 == customer5? " + customer4.equals(customer5));
}
}
测试结果:
法二:最多有max_num种套餐,按照索引参数确定是哪种套餐
代码如下:
public class KFC {
private static ArrayList<TaoCan> taocan = new ArrayList<TaoCan>();
static int max_num = 3;
static{
for(int i = 0; i < max_num; i++){
taocan.add(new TaoCan());
}
}
public static TaoCan getinstance(final int i){//最多有max_num种套餐,如果调用次数超过,则默认为最后一种
synchronized (KFC.class) {
if(i <= max_num){
return taocan.get(i-1);
} else {
System.out.println("对不起,本店没有该套餐。。。 i = " + i);
return null;
}
}
}
}
测试类:
package KFC;
public class Customer {
public static void main(String[] args) {
KFC kfc = new KFC();
TaoCan customer1 = kfc.getinstance(1);
TaoCan customer2 = kfc.getinstance(2);
TaoCan customer3 = kfc.getinstance(3);
TaoCan customer4 = kfc.getinstance(4);
TaoCan customer5 = kfc.getinstance(5);
TaoCan customer6 = kfc.getinstance(2);
if(customer1 != null && customer2 != null)
System.out.println("customer1 == customer2? " + customer1.equals(customer2));
if(customer1 != null && customer3 != null)
System.out.println("customer1 == customer3? " + customer1.equals(customer3));
if(customer2 != null && customer3 != null)
System.out.println("customer2 == customer3? " + customer2.equals(customer3));
if(customer3 != null && customer5 != null)
System.out.println("customer3 == customer5? " + customer3.equals(customer5));
if(customer4 != null && customer5 != null)
System.out.println("customer4 == customer5? " + customer4.equals(customer5));
if(customer6 != null && customer2 != null)
System.out.println("customer6 == customer2? " + customer6.equals(customer2));
}
}
测试结果:
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