For your advice on the Calulator so far developed

[Varuna Seneviratna]

The following is the class which contains Arithmetic Logic and the Test class. Please advice me on the development and the areas I should improve when designing an application

/**
 * This class is to perform normal Arithmetic calculation
 * like Addition, subtraction, division and multiplication.
 * For now it performs only addition and subtraction
 *
 *
 * @author Varuna Seneviratna
 * @version 19 June 2009
 */
public class ArithmaticLogicUnit
{
 

    private char operator;
    private char previousOperator;
    private int currentValue;
    private int finalValue;
    private int inputNumber;
   

    /**
     * Displays the final value
     *
     * @param void
     * @return int currentValue
     */
    public int getfinalValue()
    {
        return finalValue;
    }
   
    /**
     * The input number is taken in and the operation to
     * perform is invorked
     *
     * @param int number
     * @return void
     */
    public void inputNumber(int number)
    {
        this.inputNumber=number;
       operation();
    }
   
    /**
     * The operation to preform is assigned
     *
     * @param char operator
     * @return void
     *
     */
    public void operationToPerform(char operator)
    {
        this.operator=operator;
        operation();
    }
   
    /**
     * An operation is executed according to
     * the value of the operator and previousOperator variable
     *
     * @param void
     * @return void
     *
     */
    public void operation()
    {
        if(operator == '+' || previousOperator == '+' )
        {
            currentValue=currentValue + inputNumber;
            previousOperator=operator;
            operator =' ';
            inputNumber=0;
           
           
        }
        else if(operator == '-' || previousOperator == '-')
        {
           currentValue=currentValue - inputNumber;
            previousOperator=operator;
            operator=' ';
            inputNumber=0;
        }
        else if(operator == '=')
        {
            finalValue=currentValue;
            currentValue=0;
        }
    }
}

The below is the Test class that I have written so far for Addition and subtraction
operations

/**
 *This is the Test class for the ArithmaticLogicUnit class.
 *
 * @author Varuna Seneviratna
 * @version 19 June 2009
 */
public class TestUnit
{
    // instance variables
    private ArithmaticLogicUnit mycal;

    /**
     * Constructor for objects of class TestUnit
     */
    public TestUnit()
    {
        // initialise instance variables
        mycal = new ArithmaticLogicUnit();
    }

    /**
     *
     *
     * @param void
     * @return     the sum of x and y
     */
    public int testPlusAndSub()
    {
        mycal.inputNumber(5);
        mycal.operationToPerform('+');
        mycal.inputNumber(6);
        mycal.operationToPerform('-');
        mycal.inputNumber(6);
        mycal.operationToPerform('+');
        mycal.inputNumber(7);
        mycal.operationToPerform('=');
       // mycal.inputNumber(10);
      // mycal.operationToPerform('+');
      //  mycal.inputNumber(15);
      //  mycal.operationToPerform('-');
     //   mycal.inputNumber(30);
       // mycal.operationToPerform('=');
       // mycal.inputNumber
       // mycal.inputOperator('-');
        int finalResult=mycal.getfinalValue();
       return finalResult;
       
       
       
       
    }
}

[Max Rahder]

Is this for a school assignment or something? Why not just implement methods like add(int i), subtract(int i), etc. You'd need a single instance field -- value -- and you'd add to it or subtract from it in those methods. Much simpler. Something like:

public class Calculator {
  private int value = 0;
  public void add(int i){
    this.value += i;
  }
  public void subtract(int i){
    this.value +- i;
  }
  public int getValue(){
    return this.value;
  }
}

And your test routine would be like:

public class Test {
  private int value = 0;
  public static void main(String[] args){
    Calculator c = new Calculat0r();
    c.add(5);
    c.subtract(6);
    c.add(7);
    System.out.println(c.getValue());
  }
}

[Varuna Seneviratna]

But Max., I want be able to implement the calculator interface via this class, if I use your class is it possible.For ex:- 1 + 4 + 6 - 9=2, now in a calculator interface how can I invoke the add operation when + is pressed - operation when "- "is pressed using your class design?.
This is a exercise from the book Objects First With Java

[Max Rahder]

Varuna: Oh, it's from a book. Since the person who made it up defined certain requirements, I'd have to see what he those are to comment on your implementation. Can you copy those here? Off hand, I'd avoid passing chars, such as + and -, to methods and have the code interpret them, since those are part of the user interface. In other words, you probably still need methods like add() and subtract(). If you wanted to get very OO, then you might code an Operator class, with subclasses like Add and Subtract. These could have a do(int operand1, int operand2), method that would do subtraction or addition or whatever. In this case, your calculator, or ALU class, would have an applyOperator(Operator o) method where'd you pass that in.