calculator question

[Chad Moore]

Can someone tell me how to cascade my calculator functions.
What I mean is:
If the user clicks 1 + 2 + 3 the output should be displayed as 6.
I have to press 1 + 2 = 3 + 3 to display 6.
Otherwise it will display 5 (the last two operands added).
Here is my source code.

import java.awt.*;
import java.awt.event.*;
public class Lab4Calc
{
  //define action listener for funtion buttons
  private static class FunctionHandler implements ActionListener
  {
    public void actionPerformed (ActionEvent event)
    //Handles events from the function buttons
    {
      String whichFunction;
      op1 = Double.valueOf(inputField.getText()).doubleValue();       //get the first operand
      whichFunction = event.getActionCommand();                       //get button's name
      if (whichFunction != "equal")                                   //clears inputField if
       inputField.setText("");                                        //equal was not pressed
      else;
      //Conditional statements to determine which fucntion button was clicked
      if (whichFunction.equals("add"))
      {
        prevFunc = "add";
result = op1;
      }
      else if (whichFunction.equals("subtract"))
      {
        prevFunc = "sub";
        result = op1;
      }
      else if (whichFunction.equals("divide"))
      {
        prevFunc = "div";
        result = op1;
      }
      else if (whichFunction.equals("multiply"))
      {
        prevFunc = "mult";
        result = op1;
      }
      else if (whichFunction.equals("equal"))
      {
        equalPressed = true;
        if(prevFunc == "add")
        {
          op1 = Double.valueOf(inputField.getText()).doubleValue();   //get the second operand
          result = result + op1;
        }
       else if (prevFunc == "sub")
        {
          op1 = Double.valueOf(inputField.getText()).doubleValue();   //get the second operand
          result = result - op1;
        }
        else if (prevFunc == "mult")
        {
          op1 = Double.valueOf(inputField.getText()).doubleValue();   //get the second operand
          result = result * op1;
        }
        else if (prevFunc.equals("div"))// == "div")
        {
          op1 = Double.valueOf(inputField.getText()).doubleValue();   //get the second operand
          result = result / op1;
        }
        else;
      if (prevFunc == "div" && op1 == 0)
         inputField.setText("Can't Divide by Zero");                  //test for division by zero
      else
        inputField.setText("" + result);                              //display result
      }
    }
  }
    //define action listener for the clear button
  private static class ClearHandler implements ActionListener
  {
    public void actionPerformed(ActionEvent event)
    //handles events from the Clear button
    {
      result = 0.0;                                                   //clear result to zero
      inputField.setText("");                                         //clear input
    }
  }
    //define action listener for the numbers on the keypad
  private static class ValueHandler implements ActionListener
  {
    public void actionPerformed(ActionEvent event)
    //handles events from the numberpap
    {
      String getInput = "";
      String whichButton;
      whichButton = event.getActionCommand();                         //get button's name
      if (equalPressed == true)
      {
        inputField.setText("");
equalPressed = false;
      }
      getInput = (inputField.getText() + getInput);
      inputField.setText(getInput + whichButton);
    }
  }
    private static TextField inputField;                              //data field
    private static Frame calculatorFrame;                             //declare a frame variable
    private static double result;                                     //store current value
    private static double tempOp;
    private static double op1;
    private static String prevFunc;                                  //determines previous operation
    private static boolean equalPressed;
    public static void main (String [] args)
    {
      FunctionHandler function;                                       //declare function listener
      ClearHandler    clearFunction;                                  //declare clear listener
      ValueHandler    valueFunction;
      Label           emptyLabel;                                     //declare empty label
      Label           emptyLabel2;                                    //declare empty label
      Button          add;                                            //add button
      Button          subtract;                                       //subtract button
      Button          multiply;                                       //multiply button
      Button          divide;                                         //divided button
      Button          clear;                                          //clear button
      Button          equal;                                          //equal button
      Button          decimal;                                        //decimal button
      Button          zero,one,two,three,four;                        //numbers 1-4
      Button          five,six,seven,eight,nine;                      //numbers 5-9
      Button          blank;
      function = new FunctionHandler();                               //instantiate function
      clearFunction = new ClearHandler();
      result = 0.0;                                                   //instantiate result
      valueFunction = new ValueHandler();
      //instantiate labels and initialize input field
      calculatorFrame = new Frame();
      calculatorFrame.setLayout(new GridLayout (5,0,8,8));
      inputField = new TextField("",15);
      inputField.setEditable(false);
      inputField.setForeground(Color.black.darker().darker());
      emptyLabel = new Label("Chad's",Label.CENTER);
      emptyLabel.setBackground(Color.green.darker());
      emptyLabel2 = new Label("Calculator",Label.CENTER);
      emptyLabel2.setBackground(Color.green.darker());
      //instantiate button objects
      zero = new Button("0");                 zero.setBackground(Color.cyan);
      one = new Button("1");                  one.setBackground(Color.cyan);
      two = new Button("2");                  two.setBackground(Color.cyan);
      three = new Button("3");                three.setBackground(Color.cyan);
      four = new Button("4");                 four.setBackground(Color.cyan);
      five = new Button("5");                 five.setBackground(Color.cyan);
      six = new Button("6");                  six.setBackground(Color.cyan);
      seven = new Button("7");                seven.setBackground(Color.cyan);
      eight = new Button("8");                eight.setBackground(Color.cyan);
      nine = new Button("9");                 nine.setBackground(Color.cyan);
      decimal = new Button(".");              decimal.setBackground(Color.cyan);
      equal = new Button ("=");               equal.setBackground(Color.orange);
      add = new Button ("+");                 add.setBackground(Color.orange);
      subtract = new Button ("-");            subtract.setBackground(Color.orange);
      multiply = new Button ("*");            multiply.setBackground(Color.orange);
      divide = new Button ("/");              divide.setBackground(Color.orange);
      clear = new Button ("CE");              clear.setBackground(Color.orange);
      //name button events                     //Register the button Listeners
      zero.setActionCommand("0");              zero.addActionListener(valueFunction);
      one.setActionCommand("1");               one.addActionListener(valueFunction);
      two.setActionCommand("2");               two.addActionListener(valueFunction);
      three.setActionCommand("3");             three.addActionListener(valueFunction);
      four.setActionCommand("4");              four.addActionListener(valueFunction);
      five.setActionCommand("5");              five.addActionListener(valueFunction);
      six.setActionCommand("6");               six.addActionListener(valueFunction);
      seven.setActionCommand("7");             seven.addActionListener(valueFunction);
      eight.setActionCommand("8");             eight.addActionListener(valueFunction);
      nine.setActionCommand("9");              nine.addActionListener(valueFunction);
      decimal.setActionCommand(".");           decimal.addActionListener(valueFunction);
      add.setActionCommand("add");             add.addActionListener(function);
      subtract.setActionCommand("subtract");   subtract.addActionListener(function);
      divide.setActionCommand("divide");       divide.addActionListener(function);
      multiply.setActionCommand("multiply");   multiply.addActionListener(function);
      equal.setActionCommand("equal");         equal.addActionListener(function);
      clear.setActionCommand("clear");         clear.addActionListener(clearFunction);
      //add interface elements to calculatorFrame
      calculatorFrame.add(inputField);
      calculatorFrame.add(emptyLabel);
      calculatorFrame.add(emptyLabel2);
      calculatorFrame.add(clear);
      calculatorFrame.add(seven);
      calculatorFrame.add(eight);
      calculatorFrame.add(nine);
      calculatorFrame.add(divide);
      calculatorFrame.add(four);
      calculatorFrame.add(five);
      calculatorFrame.add(six);
      calculatorFrame.add(multiply);
      calculatorFrame.add(one);
      calculatorFrame.add(two);
      calculatorFrame.add(three);
      calculatorFrame.add(subtract);
      calculatorFrame.add(zero);
      calculatorFrame.add(decimal);
      calculatorFrame.add(equal);
      calculatorFrame.add(add);
      calculatorFrame.pack();
      calculatorFrame.show();
      calculatorFrame.addWindowListener(new WindowAdapter()
      //define window closing even handler
        {
          public void windowClosing(WindowEvent event)
          {
            calculatorFrame.dispose();
            System.exit(0);
          }
        });
  }
}

[ March 07, 2002: Message edited by: Chad Moore ]

[Junilu Lacar]

Have you studied Finite State Machines yet?
Junilu
[ March 08, 2002: Message edited by: Junilu Lacar ]

[Chad Moore]

No ??

[Junilu Lacar]

No ??
The reason I asked is because a Calculator is normally implemented as a Finite State Machine. Other topics that would be good for you to know about are stacks and Reverse Polish Notation. This is obviously coursework so I was just wondering if FSMs and RPN is something that you have already encountered in your studies.
There are quite a number of things you can do to improve your program. I know this is not what you asked originally but IMO it would be well worth the effort to refactor your design before adding new functionality. When you do get around to adding new functionality you can do it easily and naturally.
Do you want to give it a shot? I'd be happy to step you through. But if you'd rather just get the lab work done, I'm sure others could suggest a quicker fix.
Junilu

[Dirk Schreckmann]

Hello,
I'm salivating at the prospect of learning some great design concepts. Chad, please accept the offer from Junilu or I'll have to post some really sloppy code to try and lure critique.
Good Luck,
-Dirk Schreckmann

[Manfred Leonhardt]

Hi Chad,
I can get you somewhere near (about 90%) using your existing code. I would just do the following three things:
1. Dump your result variable
2. Assign variable op1 Double.MAX_VALUE as a default and whenever we want to clear it.
3. Make better use of equalPressed boolean. You can use it for any operation pressed.
The code below gets really close.

  //define action listener for function buttons  
  private static class FunctionHandler implements ActionListener  
  {    
    public void actionPerformed( ActionEvent event )    
    {      
      String outputString = "";
      double secondOperand = Double.MAX_VALUE;
      String inputString = inputField.getText();
      String whichFunction = event.getActionCommand();
      //
      // Read in first operand from textfield
      // If we get a good one clear the textfield.
      //
      if( inputString != null && inputString.length() > 0 )
      {
        if( op1 == Double.MAX_VALUE )
        {
          if( !inputString.equals( "Error" ) )
          {
            op1 = Double.valueOf( inputString ).doubleValue();
          }
          equalPressed = true;
        }
        else if( !equalPressed )
        {
          secondOperand = Double.valueOf( inputString ).doubleValue();
          equalPressed = true;
          if( prevFunc.equals( "add" ) )
          {
            op1 += secondOperand;
            outputString = new Double( op1 ).toString();
          }
          else if( prevFunc.equals( "subtract" ) )
          {
            op1 -= secondOperand;
            outputString = new Double( op1 ).toString();
          }
          else if( prevFunc.equals( "divide" ) )
          {
            if( secondOperand != 0. )
            {
              op1 /= secondOperand;
              outputString = new Double( op1 ).toString();
            }
            else
            {
              outputString = "Error";
              op1 = Double.MAX_VALUE;
            }
          }
          else if( prevFunc.equals( "multiply" ) )
          {
            op1 *= secondOperand;
            outputString = new Double( op1 ).toString();
          }
          inputField.setText( outputString );
        }
        if( !whichFunction.equals( "equal" ) &&
            !inputString.equals( "Error" ) )
        {
          prevFunc = whichFunction;
        }
      }  
    }
  }
  //define action listener for the clear button  
  private static class ClearHandler implements ActionListener  
  {    
    public void actionPerformed(ActionEvent event)    
      //handles events from the Clear button    
    {      
      op1 = Double.MAX_VALUE;
      inputField.setText(""); 
    }  
  }

Enjoy,
Manfred.

[Chad Moore]

Manfred, thanks for taking the time to look at and alter my code. Junilu, as Dirk stated, I would like to learn some programming concepts that will give me more programming skills. The calculator was already turned in, but I would still like to work on it more. It was a quite a learning experience, so I think it would help even more to continue with it. Being new to Java and OOP for that matter, I will take all the help I can get.
Thanks again

[Junilu Lacar]

Great! I'll start a thread in OO, Patterns, and Refactoring tonight so check it out there.
Junilu
[ March 09, 2002: Message edited by: Junilu Lacar ]