effective-java学习笔记---使用接口模拟可扩展的枚举38

 1 // Emulated extensible enum using an interface
 2 public interface Operation {
 3     double apply(double x, double y);
 4 }
 5 
 6 // Emulated extension enum
 7 public enum ExtendedOperation implements Operation {
 8     EXP("^") {
 9         public double apply(double x, double y) {
10             return Math.pow(x, y);
11         }
12     },
13     REMAINDER("%") {
14         public double apply(double x, double y) {
15             return x % y;
16         }
17     };
18 
19     private final String symbol;
20     ExtendedOperation(String symbol) {
21         this.symbol = symbol;
22     }
23     @Override 
24     public String toString() {
25         return symbol;
26     }
27 }              

public static void main(String[] args) {
　　double x = Double.parseDouble(args[0]);
　　double y = Double.parseDouble(args[1]);
　　test(ExtendedOperation.class, x, y);
}

private static <T extends Enum<T> & Operation> void test(Class<T> opEnumType, double x, double y) {
　　　　for (Operation op : opEnumType.getEnumConstants()){

　　　　　　System.out.printf("%f %s %f = %f%n",x, op, y, op.apply(x, y));

　　　　}

}

public static void main(String[] args) {
　　double x = Double.parseDouble(args[0]);
　　double y = Double.parseDouble(args[1]);
　　test(Arrays.asList(ExtendedOperation.values()), x, y);
}
private static void test(Collection<? extends Operation> opSet,double x, double y) {
　　for (Operation op : opSet)
　　　　System.out.printf("%f %s %f = %f%n",x, op, y, op.apply(x, y));
}