basic telephone keypad

[joey whitewolfe]

how do I build a basic java application of a telephone keypad and add a label at the bottom saying what I want it to say? I've tried and this is what I've come up with so far but it doesn't work
my code

import java.awt.*;
import java.awt.event.*;
 
public class Telephone extends Frame implements ActionListener
{
    private Button keysArray[];
    private Panel keyPad;
    private TextField lcdField;
    private boolean first;
    private boolean foundKey;
    private static boolean clearText;
    private int prevOperator;
    
    public Telephone()
    {
        lcdField = new TextField(20);
        keyPad = new Panel();
        keysArray = new Button[12];
        prevOperator = 0;
        first = true;
        clearText = true;
        
        //Create the layout
        setBackground(Color.magenta);
        setLayout(new BorderLayout());
        lcdField.setEditable(false);
        add("South",  new Label("Click each button above to dial your number"));
        
        //Set panel layout manager
        keyPad.setLayout(new GridLayout(4,3,10,10));
        
        //Add buttons to keyPad panel
        for  (int  i = 1;  i <= 3;  i++)  //adds buttons 1, 2, and 3 to Panel
        keyPad.add(keysArray[i]);
        
        for (int i = 4;  i <= 6;  i++)    //adds buttons 4, 5, and 6 to Panel
        keyPad.add(keysArray[i]);
        
        for (int i = 7;  i <= 9;  i++)    //adds buttons 7, 8, 9, to Panel
        keyPad.add(keysArray[i]);
        
        keyPad.add(keysArray[10]);       //adds multiply button to Panel
        
        keyPad.add(keysArray[11]);      //adds 0 key to Panel
        
        keyPad.add(keysArray[12]);      //adds number key to Panel
        
        add(lcdField, BorderLayout.NORTH);
        add(keyPad, BorderLayout.CENTER);
        
        addWindowListener(
        new WindowAdapter()
            {
                public void windowClosing(WindowEvent e)
                {
                    System.exit(0);
                }
            }
        );
    }
    
    public void actionPerformed(ActionEvent e)
    {
        foundKey = false;
        
        //Search for the key pressed
        for (int  i = 1;  i < keysArray.length && !foundKey;  i++)
            if(e.getSource() == keysArray[i])                //key match found
            {
                foundKey = true;
                switch(i)
                {
                    case 1: case 2: case 3: case 4:         //number buttons
                    case 5: case 6: case 7: case 8: case 9:         //1  - 12
                    case 10: case 11: case 12:
                    if(clearText)
                    {
                        lcdField.setText("");
                        clearText = false;
                    }
                    lcdField.setText(lcdField.getText() + keysArray[i].getLabel());
                    break;
                }
            }
    }
    
    public static void main(String args[])
    {
        //Create a new instance of the Telephone object
        Telephone teleFrame = new Telephone();
        
        //Set frame attributes
        teleFrame.setBounds(50,100,200,300);
        teleFrame.setTitle("Telephone");
        teleFrame.setVisible(true);
    }
}

[ edited to preserve formatting using the [code] and [/code] UBB Tags -ds ]
[ September 07, 2002: Message edited by: Dirk Schreckmann ]

[Dirk Schreckmann]

how do I build a basic java application of a telephone keypad and add a label at the bottom saying what I want it to say?
I haven't looked at your code yet. Are you basically curious about how to change the displayed text of a label?

[joey whitewolfe]

i want to know how do I make this work,a functional telephone keypad with the label at the bottom of the pad could you please look over my code and help me? I am using 1.3.1platform2 I just want to do it right and make it work it doesn't have to actually dial a real number, just be based on one. It is a class project and I need help it will compile but won't run. joey

[joey whitewolfe]

when i try and run it i get these errors in dos
java.lang.nullpointer
java.awt.container.addimpl(container.java;340
223
45
339
479

[Dirk Schreckmann]

Let's start by considering the error message:

Exception in thread "main" java.lang.NullPointerException
        at java.awt.Container.addImpl(Container.java:588)
        at java.awt.Container.add(Container.java:298)
        at Telephone.<init>(Telephone.java:36)
        at Telephone.main(Telephone.java:93)

So, it's telling us that we've a problem that probably originates at line 36 or 93.
Line 36 is
keyPad.add(keysArray[i]);
and line 93 is
Telephone teleFrame = new Telephone();
Lines 36 through 48 ( keyPad.add(keysArray[12]); ) would appear to be trying to use components of an array that haven't been properly initialized. Take a good look at the code that creates and uses the array of buttons. Do you ever actually create and add new Button objects to the array? The answer is no. Do you have any ideas on how to correct this problem?
[ September 08, 2002: Message edited by: Dirk Schreckmann ]

[joey whitewolfe]

totally lost

[Barry Gaunt]

Another interesting thing is to look at how many Buttons you can put in a keyArray, and check how many you are putting into it, or taking out of it.
Also how do you know what Buttons do what? Like mine at home got digits on them. In fact I don't see any Buttons, just places to put buttons!
I know we are pi**g you around but when you see it you will be a better programmer for it
-Barry
[ September 08, 2002: Message edited by: Barry Gaunt ]

[Dirk Schreckmann]

joey,
What part is causing you confusion? Is working with arrays new for you? Are you comfortable making programs with Buttons when the Buttons aren't part of an array?

[joey whitewolfe]

yes I'm new to arrays just confussing me on the concepts

[joey whitewolfe]

when i try and run in dos i get a main thread error- is there any reason it won't run in dos?i can compile it but when i type java Telephone i get the thread error

[Dirk Schreckmann]

A few posts up, I displayed the error message that this program creates and I began to explain why this error message is created.
You may want to take some time to read and learn about using arrays in Java. The following list of sites are all decent places to have a look for such information:

Sun's Java Tutorial

Introduction to Computer Science using Java by Bradley Kjell

Introduction to Programming Using Java by David J. Eck

Dick Baldwin's Java Programming Tutorials

In a nutshell, the aforementioned error message is displayed because you have an array of Button references that don't refer to actual Button objects. You've never created any Buttons - you've only created an array of Button references (that all refer to null). Perhaps you want to use a loop structure to create new Button objects for the array of Button references to refer to.

[joey whitewolfe]

thanks I got it now!

[joey whitewolfe]

thanks guys! I was able to get it running and just wanted you to see the finished code
/*
Name:
Date:September 4, 2002
Program Name:Telephone
Purpose:Web Phone
*/
import java.awt.*;
import java.awt.event.*;
public class Telephone extends Frame implements ActionListener
{
public Button keysArray[];
public Panel keyPad;
public TextField displayField;
public boolean foundKey;
public Label bottomLabel;
public Telephone()
{
displayField = new TextField(20);
keyPad = new Panel();
keysArray = new Button[12];
Label bottomLabel = new Label("Click each button above to dial your number");
displayField.setEditable(false);
setBackground(Color.magenta);

//Set Frame Layout
setLayout(new BorderLayout());
keyPad.setLayout(new GridLayout(4,3,10,10));
//Creating Buttons
for (int i = 0; i <= 9; i++)
keysArray[i] = new Button(String.valueOf(i));
keysArray[10] = new Button("*");
keysArray[11] = new Button("#");

//adding buttons
for (int i = 1; i <= 9; i++) //adds buttons 1-9 to Panel
keyPad.add(keysArray[i]);
keyPad.add(keysArray[10]);//adds * button to Panel
keyPad.add(keysArray[0]);//adds 0 button to Panel
keyPad.add(keysArray[11]);//adds # button to Panel

add(displayField, BorderLayout.NORTH); //adds text field to top of Frame
add(keyPad, BorderLayout.CENTER);//adds the keypad
add(bottomLabel, BorderLayout.SOUTH);//adds the display at the bottom
for(int i = 0; i < keysArray.length; i++)
keysArray[i].addActionListener(this);
addWindowListener(
new WindowAdapter()
{
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
}
);
}//end of Telephone method
public void actionPerformed(ActionEvent e)
{
foundKey = false;
//Search fo the key pressed
for (int i = 0; i < keysArray.length && !foundKey; i++)
if(e.getSource() == keysArray[i])//key match found
{
displayField.setText(displayField.getText() + keysArray[i].getLabel());
}
}
public static void main(String args[])
{
//Create a new instance of the Telephone object
Telephone teleFrame = new Telephone();
//Set frame attributes
teleFrame.setBounds(50,100,260,300);
teleFrame.setTitle("Telephone");
teleFrame.setVisible(true);
}
}

[Dirk Schreckmann]

Thanks for sharing what you learned. That is the key element that makes JavaRanch so great and helps others to learn.
Note that when posting code, much of the formatting is preserved by surrounding the code with the [code] and [/code] UBB Tags.
Hope to see you 'round the Ranch!

[Barry Gaunt]

Great, Joey! There's nothing better than getting
the "AhHa" after a few pushes and shoves.
-Barry
[ September 15, 2002: Message edited by: Barry Gaunt ]

[Ron Newman]

Dirk, how did you manage to post the actual UBB tags in your message without them being interpreted?

[Dirk Schreckmann]

What, that wasn't on the SCJP exam you took?
Try using the appropriate html tags. The left bracket is &#91; and the right bracket is &#93; . Take a look at http://www.asciitable.com to find out what different ones are.
Enjoy and use this power wisely...