Thread: Simple Calculator HELP

I need help with my getDisplayValue() method. I am trying to iterate though an Array to display a value in a calculator, but I doesn't work. I keep on getting these weird magical numbers at the end of the iteration. Note that this is done in BlueJ. Thank you for all your help in advance.
Calculator -> UserInterface -> CalcEngine and Calculator -> CalcEngine.

public class CalcEngine
{
    //Instance variables used.
    //These are all the instance variables I used to implement
    //a complete calculator solution. 
 
    private int finalNumber; //Holds results of calculations to date.
    private int[] digitHold; //holds numbers pressed until they are operated on
    private int indexed;  //holds index of last number added to digitHold array
    int currentOp; //indicates operation waiting to be calculated(0=none, 1=plus, 2=minus)
 
    /**
     * Create a CalcEngine instance. Initialise its state so that it is ready 
     * for use.
     */
    public CalcEngine()
    {
        int finalNumber = 0;
        int indexed = 0;
        int currentOp = 0;
        digitHold = new int[10];
    }
 
    /**
     * A number button was pressed. Do whatever you have to do to handle it.
     * The number value of the button is given as a parameter.
     */
    public void numberPressed(int number)
    {
        digitHold[indexed] = number;
        indexed++;
    }
 
    /**
     * Return the value that should currently be displayed on the calculator
     * display. THIS ONE!!:confused::confused:
     */
    public int getDisplayValue()
    {
        int placeValue = 1;
        for(int index = digitHold.length-1; index >= 0; index--)
        {
            finalNumber += digitHold[index] * placeValue;
            placeValue = placeValue * 10;
        }
        return finalNumber/10; //for compilation purposes only
    }
 
    /**
     * The 'plus' button was pressed. 
     */
    public void plus()
    {
 
    }
 
    /**
     * The 'minus' button was pressed.
     */
    public void minus()
    {
        // doesn"t work sequentially.
    }
 
    /**
       * The '=' button was pressed.
     */
    public void equals()
    {
    }
 
    /**
     * The 'C' (clear) button was pressed.
     */
    public void clear()
    {
        finalNumber = 0;
        indexed = 0;
        currentOp = 0;
        for(int index = 0; index < 10; index++)
        {
            digitHold[index] = 0;
        }
        getDisplayValue();
 
    }
 
    /**
     * Return the title of this calculation engine.
     */
    public String getTitle()
    {
        return "Basic Calculator";
    }
 
    /**
     * Return the author of this engine. This string is displayed as it is,
     * so it should say something like "Written by H. Simpson".
     */
    public String getAuthor()
    {
        return "Written by ";
    }
 
    /**
     * Return the version number of this engine. This string is displayed as 
     * it is, so it should say something like "Version 1.1".
     */
    public String getVersion()
    {
        return "Version 1.1";
    }
 
}

Next class:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
 
public class UserInterface
	implements ActionListener
{
	private CalcEngine calc;
	private boolean showingAuthor;
 
    private JFrame frame;
	private JTextField display;
	private JLabel status;
 
	/**
	 * Create a user interface for a given calcEngine.
	 */
	public UserInterface(CalcEngine engine)
	{
		calc = engine;
		showingAuthor = true;
		makeFrame();
		frame.setVisible(true);
	}
 
	/**
	 * Make this interface visible again. (Has no effect if it is already
	 * visible.)
	 */
    public void setVisible(boolean visible)
	{
		frame.setVisible(visible);
	}
 
	/**
	 * Make the frame for the user interface.
	 */
	private void makeFrame()
	{
		frame = new JFrame(calc.getTitle());
 
		JPanel contentPane = (JPanel)frame.getContentPane();
		contentPane.setLayout(new BorderLayout(8, 8));
		contentPane.setBorder(new EmptyBorder( 10, 10, 10, 10));
 
		display = new JTextField();
		contentPane.add(display, BorderLayout.NORTH);
 
		JPanel buttonPanel = new JPanel(new GridLayout(4, 4));
			addButton(buttonPanel, "7");
			addButton(buttonPanel, "8");
			addButton(buttonPanel, "9");
			addButton(buttonPanel, "C");
			addButton(buttonPanel, "4");
			addButton(buttonPanel, "5");
			addButton(buttonPanel, "6");
			addButton(buttonPanel, "?");
			addButton(buttonPanel, "1");
			addButton(buttonPanel, "2");
			addButton(buttonPanel, "3");
			buttonPanel.add(new JLabel(" "));
			addButton(buttonPanel, "0");
			addButton(buttonPanel, "+");
			addButton(buttonPanel, "-");
			addButton(buttonPanel, "=");
		contentPane.add(buttonPanel, BorderLayout.CENTER);
 
		status = new JLabel(calc.getAuthor());
		contentPane.add(status, BorderLayout.SOUTH);
 
		frame.pack();
	}
 
	/**
	 * Add a button to the button panel.
	 */
	private void addButton(Container panel, String buttonText)
	{
		JButton button = new JButton(buttonText);
		button.addActionListener(this);
		panel.add(button);
	}
 
	/**
	 * An interface action has been performed. Find out what it was and
	 * handle it.
	 */
	public void actionPerformed(ActionEvent event)
	{
		String command = event.getActionCommand();
 
		if(command.equals("0") ||
		   command.equals("1") ||
		   command.equals("2") ||
		   command.equals("3") ||
		   command.equals("4") ||
		   command.equals("5") ||
		   command.equals("6") ||
		   command.equals("7") ||
		   command.equals("8") ||
		   command.equals("9"))
		{
			int number = Integer.parseInt(command);
			calc.numberPressed(number);
		}
		else if(command.equals("+"))
			calc.plus();
		else if(command.equals("-"))
			calc.minus();
		else if(command.equals("="))
			calc.equals();
		else if(command.equals("C"))
			calc.clear();
		else if(command.equals("?"))
			showInfo();
 
		redisplay();
	}
 
	/**
	 * Update the interface display to show the current value of the 
	 * calculator.
	 */
	private void redisplay()
	{
		display.setText("" + calc.getDisplayValue());
	}
 
	/**
	 * Toggle the info display in the calculator's status area between the
	 * author and version information.
	 */
	private void showInfo()
	{
		if(showingAuthor)
			status.setText(calc.getVersion());
		else
			status.setText(calc.getAuthor());
 
		showingAuthor = !showingAuthor;
	}
}

Next class:

public class Calculator
{
	private CalcEngine engine;
	private UserInterface gui;
 
	/**
	 * Create a new calculator and show it.
	 */
	public Calculator()
	{
		engine = new CalcEngine();
		gui = new UserInterface(engine);
	}
 
	/**
	 * In case the window was closed, show it again.
	 */
	public void show()
	{
		gui.setVisible(true);
	}
}

Please edit your post and wrap your code with code tags:
[code=java]
YOUR CODE HERE
[/code]
to get highlighting and preserve formatting.

I keep on getting these weird magical numbers

Can you copy them and paste them here.

One problem I see is that the value returned by the getDisplayValue() method is not saved in a variable.

Ok, what numbers where you expecting instead of those?

How is the code executed? I don't see the main() method in any class to start the execution.

That output was all from just entering a 9?

Try debugging the code in the getDisplayValue() method by adding some println() statements that print out the values of all the variables that the method uses as it calculates the values.
Use the Arrays class's toString() method to format the array for printing:
System.out.println("an ID "+ java.util.Arrays.toString(theArrayName));

I have already debugged the code.

How, I don't see any println() statments that would show you what the code was doing.

When you added the println() statements I suggested:
When you enter the first number say an 8:
What printed out for the contents of the array?
What printed out for the value of finalNumber?

What value should be shown in the text area?

When an 8 is entered, what should be shown in the textarea?
Debug the steps in the getDisplayValue() method that compute the value of finalNumber.
Print the value of finalNumber every time its value is changed and post it here.
Should its value be 8?

Also print these values:
what's in finalNumber when the method starts executing?
the value of placeValue every time it is changed inside the loop

Press 2 instead of 8

Can you see what the code is doing? It is ALWAYS multiplying the numbers 10 times ONCE for each slot in the array. Shouldn't it just use what has been entered?

The reason the numbers go weird is that an int holds a max value of 2 billion. Larger numbers are truncated leaving whatever.

Your debug print out needs both finalNumber and placeValue every time they are changed so you can see what is happening.

What is the value of finalNumber when the second button is pressed?
Continue debugging that method so you see what it is doing.

I'm done for tonight. Back tomorrow.