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));	}}