1 package com.twoslow.cha6;2 3 public interface OperationInterface {4 5     double apply(double x , double y) ;6 }

 1 package com.twoslow.cha6; 2  3 public enum BaseOperation implements OperationInterface{ 4  5     PLUS("+"){ 6         public double apply(double x , double y ) {return x + y ;} 7     }, 8     MINUS("-"){ 9         public double apply(double x , double y ) {return x - y ;}10     },11     TIMES("*"){12         public double apply(double x , double y ) {return x * y ;}13     },14     DIVIDE("/"){15         public double apply(double x , double y ) {return x / y ;}16     } ;17     18     private final String symbol ;19     20     BaseOperation(String symbol) {21         this.symbol = symbol ;22     }23 }

 1 package com.twoslow.cha6; 2  3 public enum ExtendedOperation implements OperationInterface{ 4  5     EXP("^") { 6         public double apply(double x, double y){return Math.pow(x, y) ;}; 7     } , 8      9     REMAINDER("%") {10         public double apply(double x , double y ) {return x % y ;} ;11     } ;12     13     14     private final String symbol ;15     16     ExtendedOperation(String symbol) {17         this.symbol = symbol ;18     }19 }

 1 package com.twoslow.cha6; 2  3 import java.util.Arrays; 4 import java.util.Collection; 5  6 public class MainTest { 7  8     public static void main(String[] args) { 9 //        test(ExtendedOperation.class , 3,2) ;10         11         test2(Arrays.asList(BaseOperation.values()),3,2) ;12     }13     14     //泛型声明确保对象既表示枚举又表示Operation的子类型15     private static <T extends Enum<T> & OperationInterface> void test(Class<T> opSet , double x , double y ) {16         for(OperationInterface op : opSet.getEnumConstants()) {17             System.out.println(op.apply(x, y));18         }19     }20     21     private static  void test2(Collection<? extends OperationInterface> opSet , double x , double y ) {22         for(OperationInterface op : opSet) {23             System.out.println(op.apply(x, y));24         }25     }26 }