simple_calculator.mj

program SimpleCalculator
  const char SPACE  = ' ';
  const char EQUALS  = '=';

  class Calculator {
    int operand1;
    int operand2;
    int result;
    {
      void setOperand1(int operand) {
        this.operand1 = operand;
      }
      void setOperand2(int operand) {
        this.operand2 = operand;
      }
      int generateResult() {
        return 0;
      }
      void calculate() {
        this.result = this.generateResult();
      }
      int getOperand1() {
        return this.operand1;
      }
      int getOperand2() {
        return this.operand2;
      }
      int getResult() {
        return this.result;
      }
    }
  }

  class AdditionCalculator extends Calculator {
      {
        int generateResult() {
          return this.operand1 + this.operand2;
        }
      }
  }

  class SubtractionCalculator extends Calculator {
    {
      int generateResult() {
        return this.operand1 - this.operand2;
      }
    }
  }

  class MultiplicationCalculator extends Calculator {
    {
      int generateResult() {
          return this.operand1 * this.operand2;
      }
    }
  }

  class DivisionCalculator extends Calculator {
    {
      int generateResult() {
          return this.operand1 / this.operand2;
      }
    }
  }

{
  void main()
  int operand1, operand2;
  char operator;
  int numExpressions;
  Calculator calculator;
  AdditionCalculator additionCalculator;
  SubtractionCalculator subtractionCalculator;
  MultiplicationCalculator multiplicationCalculator;
  DivisionCalculator divisionCalculator;
  {
    numExpressions = 4;
    additionCalculator = new AdditionCalculator;
    subtractionCalculator = new SubtractionCalculator;
    multiplicationCalculator = new MultiplicationCalculator;
    divisionCalculator = new DivisionCalculator;
    do {
      read(operand1);
      read(operator);
      read(operand2);
      if (operator == '+') {
        calculator = additionCalculator;
      } else if (operator == '-') {
        calculator = subtractionCalculator;
      } else if (operator == '*') {
        calculator = multiplicationCalculator;
      } else if (operator == '/') {
        calculator = divisionCalculator;
      }
      calculator.setOperand1(operand1);
      calculator.setOperand2(operand2);
      calculator.calculate();
      print(operand1);
      print(SPACE);
      print(operator);
      print(SPACE);
      print(operand2);
      print(SPACE);
      print(EQUALS);
      print(SPACE);
      print(calculator.getResult());
      print(eol);
      numExpressions--;
    } while (numExpressions > 0);
  }
}