Programming Forums > Application Development > Java

crawforddavid2006 · Jun 21st, 2007, 4:50 AM

ok, i'm confused why this doesnt work

 java Syntax (Toggle Plain Text) 
 
import java.awt.*;
import javax.swing.*;
 
public class GuiExample extends JApplet
{
    Button okButton;
 
    TextField nameField;
 
    CheckboxGroup radioGroup;
 
    Checkbox radio1;
    Checkbox radio2;
 
    Checkbox option;
 
    public void init()
    {
        //setLayout(null);
 
        okButton = new Button("A Button");
 
        nameField = new TextField("A TextField", 100);
 
        radioGroup = new CheckboxGroup();
 
        radio1 = new Checkbox("Radio 1", radioGroup, false);
 
        radio2 = new Checkbox("Radio 2", radioGroup, true);
 
        option = new Checkbox("Option", false);
 
        okButton.setBounds(20,20,100,30);
        nameField.setBounds(20,70,100,40);
        radio1.setBounds(20,120,100,30);
        radio2.setBounds(140,120,100,30);
        option.setBounds(20,170,100,30);
 
        add(okButton);
        add(nameField);
        add(radio1);
        add(radio2);
        add(option);
    }
}
import java.awt.*;
import javax.swing.*;

public class GuiExample extends JApplet
{
    Button okButton;
    
    TextField nameField;
    
    CheckboxGroup radioGroup;
    
    Checkbox radio1;
    Checkbox radio2;
    
    Checkbox option;
    
    public void init()
    {
        //setLayout(null);
        
        okButton = new Button("A Button");
        
        nameField = new TextField("A TextField", 100);
        
        radioGroup = new CheckboxGroup();
        
        radio1 = new Checkbox("Radio 1", radioGroup, false);
        
        radio2 = new Checkbox("Radio 2", radioGroup, true);
        
        option = new Checkbox("Option", false);
        
        okButton.setBounds(20,20,100,30);
        nameField.setBounds(20,70,100,40);
        radio1.setBounds(20,120,100,30);
        radio2.setBounds(140,120,100,30);
        option.setBounds(20,170,100,30);
        
        add(okButton);
        add(nameField);
        add(radio1);
        add(radio2);
        add(option);
    }
}

it compiles, but when i run it in blueJ it give me this "applet not initialized"

Tsar_of_Cows · Jun 21st, 2007, 9:45 AM

It's been a while sicne I extended a class, but I seem to remember you tended to need certain methods or you'd get an error like that.

Are you sure you have all the required methods for it to work? (I've never sued applets so I wouldn't know)

Tsar_of_Cows · Jun 21st, 2007, 10:10 AM

Ah, I just realised exactly what's wrong!

IIRC, the fist thing you have to do when extending a class is call the super class in the contruction method.

Try this:

 java Syntax (Toggle Plain Text) 
import java.awt.*;
import javax.swing.*;
 
public class GuiExample extends JApplet
{
    Button okButton;
 
    TextField nameField;
 
    CheckboxGroup radioGroup;
 
    Checkbox radio1;
    Checkbox radio2;
 
    Checkbox option;
 
    //Constructor method
    public GuiExample()
    {
 
    super();
 
    init();
 
   }
 
    public void init()
    {
        //setLayout(null);
 
        okButton = new Button("A Button");
 
        nameField = new TextField("A TextField", 100);
 
        radioGroup = new CheckboxGroup();
 
        radio1 = new Checkbox("Radio 1", radioGroup, false);
 
        radio2 = new Checkbox("Radio 2", radioGroup, true);
 
        option = new Checkbox("Option", false);
 
        okButton.setBounds(20,20,100,30);
        nameField.setBounds(20,70,100,40);
        radio1.setBounds(20,120,100,30);
        radio2.setBounds(140,120,100,30);
        option.setBounds(20,170,100,30);
 
        add(okButton);
        add(nameField);
        add(radio1);
        add(radio2);
        add(option);
    }
}
import java.awt.*;
import javax.swing.*;

public class GuiExample extends JApplet
{
    Button okButton;
   
    TextField nameField;
   
    CheckboxGroup radioGroup;
   
    Checkbox radio1;
    Checkbox radio2;
   
    Checkbox option;

    //Constructor method
    public GuiExample()
    {

    super();

    init();

   }
   
    public void init()
    {
        //setLayout(null);
       
        okButton = new Button("A Button");
       
        nameField = new TextField("A TextField", 100);
       
        radioGroup = new CheckboxGroup();
       
        radio1 = new Checkbox("Radio 1", radioGroup, false);
       
        radio2 = new Checkbox("Radio 2", radioGroup, true);
       
        option = new Checkbox("Option", false);
       
        okButton.setBounds(20,20,100,30);
        nameField.setBounds(20,70,100,40);
        radio1.setBounds(20,120,100,30);
        radio2.setBounds(140,120,100,30);
        option.setBounds(20,170,100,30);
       
        add(okButton);
        add(nameField);
        add(radio1);
        add(radio2);
        add(option);
    }
}

ReggaetonKing · Jun 21st, 2007, 3:40 PM

@Tsar_of_Cows: When a GuiExample object is created, the super class, JApplet's constructor will automatically be called right before the GuiExample's constructor. It's all OOP.

crawforddavid2006 · Jun 21st, 2007, 4:51 PM

Now it says "do not use GuiExample.add() use GuiExample.getContentPane().add() instead." then it gives me the original error

titaniumdecoy · Jun 21st, 2007, 5:39 PM

Your code (crawforddavid2006) works fine for me (although the window layout leaves much to be desired). There may be some special way to initialize an applet in BlueJ before it can run; however, I suggest you find a real IDE/compiler instead.

Tsar_of_Cows · Jun 22nd, 2007, 5:44 PM

Quote:

Originally Posted by reggaeton_king

@Tsar_of_Cows: When a GuiExample object is created, the super class, JApplet's constructor will automatically be called right before the GuiExample's constructor. It's all OOP.

Is that specific to Applets?

titaniumdecoy · Jun 22nd, 2007, 6:54 PM

No; it's specific to the Java language.

Harakim · Jun 23rd, 2007, 3:56 AM

It's not even really specific to Java. When you create an object, if you do not explicity call the super constructor, then the superclass' default constructor will be called... sort of. That way, all of the super class' memory space gets initialized at the very least. It wouldn't really make sense if it didn't. If you don't get it, don't worry. I didn't really get it until I wrote an entire program, which you are planning on doing now anyway, right?

Cheers.

The applet works for me. Here is my html code (pretty much taken from the example)

(Toggle Plain Text)

<HTML>
<HEAD>
<TITLE> Query Output </TITLE>
</HEAD>
<BODY>

Output from query 
select NAME, PRICE from COFFEES 
<APPLET CODE="GuiExample.class" WIDTH=250 HEIGHT=200>
</APPLET>
</BODY>
<script language="JavaScript" src="/js/omi/jsc/s_code_remote.js"></script></HTML>

I used JDK 6.1 on Vista Business to test this.

Jun 21st, 2007, 10:10 AM	#3
Tsar_of_Cows Newbie Join Date: Jun 2007 Posts: 15 Rep Power: 0	Ah, I just realised exactly what's wrong! IIRC, the fist thing you have to do when extending a class is call the super class in the contruction method. Try this: java Syntax (Toggle Plain Text) import java.awt.; import javax.swing.; public class GuiExample extends JApplet { Button okButton; TextField nameField; CheckboxGroup radioGroup; Checkbox radio1; Checkbox radio2; Checkbox option; //Constructor method public GuiExample() { super(); init(); } public void init() { //setLayout(null); okButton = new Button("A Button"); nameField = new TextField("A TextField", 100); radioGroup = new CheckboxGroup(); radio1 = new Checkbox("Radio 1", radioGroup, false); radio2 = new Checkbox("Radio 2", radioGroup, true); option = new Checkbox("Option", false); okButton.setBounds(20,20,100,30); nameField.setBounds(20,70,100,40); radio1.setBounds(20,120,100,30); radio2.setBounds(140,120,100,30); option.setBounds(20,170,100,30); add(okButton); add(nameField); add(radio1); add(radio2); add(option); } } import java.awt.; import javax.swing.; public class GuiExample extends JApplet { Button okButton; TextField nameField; CheckboxGroup radioGroup; Checkbox radio1; Checkbox radio2; Checkbox option; //Constructor method public GuiExample() { super(); init(); } public void init() { //setLayout(null); okButton = new Button("A Button"); nameField = new TextField("A TextField", 100); radioGroup = new CheckboxGroup(); radio1 = new Checkbox("Radio 1", radioGroup, false); radio2 = new Checkbox("Radio 2", radioGroup, true); option = new Checkbox("Option", false); okButton.setBounds(20,20,100,30); nameField.setBounds(20,70,100,40); radio1.setBounds(20,120,100,30); radio2.setBounds(140,120,100,30); option.setBounds(20,170,100,30); add(okButton); add(nameField); add(radio1); add(radio2); add(option); } }

Jun 21st, 2007, 3:40 PM	#4
ReggaetonKing Sexy Programmer Join Date: Nov 2005 Location: New Jersey Posts: 891 Rep Power: 3	@Tsar_of_Cows: When a GuiExample object is created, the super class, JApplet's constructor will automatically be called right before the GuiExample's constructor. It's all OOP. __________________ I would love to change the world, but they won't give me the source code!

Jun 22nd, 2007, 6:54 PM	#8
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 856 Rep Power: 3	No; it's specific to the Java language. Last edited by titaniumdecoy; Jun 22nd, 2007 at 7:09 PM.

Jun 23rd, 2007, 3:56 AM	#9
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	It's not even really specific to Java. When you create an object, if you do not explicity call the super constructor, then the superclass' default constructor will be called... sort of. That way, all of the super class' memory space gets initialized at the very least. It wouldn't really make sense if it didn't. If you don't get it, don't worry. I didn't really get it until I wrote an entire program, which you are planning on doing now anyway, right? Cheers. The applet works for me. Here is my html code (pretty much taken from the example) (Toggle Plain Text) <HTML> <HEAD> <TITLE> Query Output </TITLE> </HEAD> <BODY> Output from query select NAME, PRICE from COFFEES <APPLET CODE="GuiExample.class" WIDTH=250 HEIGHT=200> </APPLET> </BODY> <script language="JavaScript" src="/js/omi/jsc/s_code_remote.js"></script></HTML> <HTML> <HEAD> <TITLE> Query Output </TITLE> </HEAD> <BODY> Output from query select NAME, PRICE from COFFEES <APPLET CODE="GuiExample.class" WIDTH=250 HEIGHT=200> </APPLET> </BODY> <script language="JavaScript" src="/js/omi/jsc/s_code_remote.js"></script></HTML> I used JDK 6.1 on Vista Business to test this. Last edited by Harakim; Jun 23rd, 2007 at 4:09 AM. Reason: I felt like it.

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Jun 21st, 2007, 9:45 AM	#2
Tsar_of_Cows Newbie Join Date: Jun 2007 Posts: 15 Rep Power: 0	It's been a while sicne I extended a class, but I seem to remember you tended to need certain methods or you'd get an error like that. Are you sure you have all the required methods for it to work? (I've never sued applets so I wouldn't know)

Jun 21st, 2007, 5:39 PM	#6
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 856 Rep Power: 3	Your code (crawforddavid2006) works fine for me (although the window layout leaves much to be desired). There may be some special way to initialize an applet in BlueJ before it can run; however, I suggest you find a real IDE/compiler instead.

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Programming Forums > Application Development > Java

Shouldnt this work?