DOS Calculator

public class Calculator {

         public static abstract class Operation {

         private final String name;

       

         Operation(String name) { this.name = name; }

       

         public String toString() { return this.name; }

       

         // Perform arithmetic op represented by this constant

         abstract double eval(double x, double y);

       

         // Doubly nested anonymous classes

             public static final Operation PLUS = new Operation("+") {

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

         };

             public static final Operation MINUS = new Operation("-") {

             double eval(double x, double y) { return x - y; }

         };

             public static final Operation TIMES = new Operation("*") {

             double eval(double x, double y) { return x * y; }

         };

             public static final Operation DIVIDE = new Operation("/") {

             double eval(double x, double y) { return x / y; }

         };

     }

   

     // Return the results of the specified calculation

         public double calculate(double x, Operation op, double y) {

         return op.eval(x, y);

     }

}

    public class CalcTest {

         public static void main(String args[]) {

         double x = Double.parseDouble(args[0]);

         double y = Double.parseDouble(args[1]);

       

         operate(x, Calculator.Operation.PLUS, y);

         operate(x, Calculator.Operation.MINUS, y);

         operate(x, Calculator.Operation.TIMES, y);

         operate(x, Calculator.Operation.DIVIDE, y);

     }

   

         static void operate(double x, Calculator.Operation op, double y) {

         Calculator c = new Calculator();

         System.out.println(x + " " + op + " " + y + " = " +

         c.calculate(x, op, y));

     }

}