java_包含抽象方法的枚举类

package ming;

enum Operation {
	PLUS {

		public double eval(double x, double y) {
			return x + y;
		}

	},
	MINS {

		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) {
			if (y == 0) {
				return -1;
			}
			return x / y;
		}
	};
	//为枚举类定义抽象方法，具体由枚举值提供实现
	public abstract double eval(double x, double y);

}

public class OperationTest {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		System.out.println(Operation.PLUS.eval(1, 2));
		System.out.println(Operation.DIVIDE.eval(1, 0));

	}

}