包含抽象方法的枚举类

public enum Operation
{
        PLUS,MINUS,TIMES,DIVIDE;//每一个枚举值都是一个实例
        double eval(double x,double y)//我们定义一个方法，实现不同的操作
        {
                switch(this)
                {
                        case PLUS: return x + y;
                        case MINUS: return x - y;
                        case TIMES: return x * y;
                        case DIVIDE: return x % y;
                        default: return 0;
                }
        }
        public static void main(String[] args)
        {
                System.out.println(Operation.PLUS.eval(3,4));
                System.out.println(Operation.MINUS.eval(3,4));
                System.out.println(Operation.TIMES.eval(3,4));
                System.out.println(Operation.DIVIDE.eval(32,4));
        }
}

[[email protected] java]# java Operation
7.0
-1.0
12.0
0.0

下面如果我们想使用内部类来解决呢？

public enum Operation2
{
        PLUS
        {
                public double eval(double x,double y)
                {
                        return x + y;
                }
        },//为什么这里会有一个，号呢？看了匿名内部类，你就会明白
        MINUS
        {
                public double eval(double x,double y)
                {
                        return x - y;
                }
        },
        TIMES
        {
                public double eval(double x ,double y)
                {
                        return x * y;
                }
        },
        DIVIDE
        {
                public double eval(double x,double y)
                {
                        return x % y;
                }
        };
        //为枚举类定义了一个抽象方法
        //这个抽象方法由不同的枚举值提供不同的实现
        public abstract double eval(double x,double y);
        public static void main(String[] args)
        {
                System.out.println(Operation2.PLUS.eval(3,4));
                System.out.println(Operation2.MINUS.eval(3,4));
                System.out.println(Operation2.TIMES.eval(3,4));
                System.out.println(Operation2.DIVIDE.eval(3,4));
        }
}

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