Enum实现单例模式

package com.wjy.effective;
 
public enum Singleton {
    INSTANCE;
 
    private int numa;
    private int numb;
    public int add(int a,int b){
        numa=a;
        numb=b;
        return numa+numb;
    }
}

客户端代码：

package com.wjy.effective;
 
public class TestSingleton {
    public static void main(String args[]){
        Singleton instance=Singleton.INSTANCE;
        int sum=instance.add(, );
 
        System.out.println("result is: "+(sum+));
    }
}

运行结果：

result is: