Chapter 6: enumeration and annotation. Item34: use interfaces to simulate scalable enumeration.

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 // The generic declaration ensures that the object represents both enumeration and operation subtype 15 private static <t extends Enum <t> & operationinterface> void test (class <t> opset, double X, doub Le 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}

 

Chapter 6: enumeration and annotation. Item34: use interfaces to simulate scalable enumeration.