Java unknown exceptions

Question

Can anyone please tell me why I get the following exceptions

Exception in thread "main" java.lang.IllegalArgumentException adding a window to a container :
 java.awt.Container.checkNotAWindow(Unknown Source) 
 java.awt.Container.addImpl(Unknown Source)  
 java.awt.Container.add(Unknown Source)         
 javax.swing.JFrame.addImpl(Unknown Source)
 java.awt.Container.add(Unknown Source)
 clockframe.<init>(clockframe.java:14)
 clockframe.main(clockframe.java:32)

My code which is inside clockpanel.java file is below: I am beginner so I don't know how to work this out......

    import java.awt.*;
    import javax.swing.*;

    public class clockframe extends JFrame
    {
      public clockframe()
      {
        super("Clock");
        setLookAndFeel();
        setSize(225, 125);
        FlowLayout flo = new FlowLayout();
        setLayout(flo);
        clockpanel time = new clockpanel();
        add(time);
        setVisible(true);
      }

      private void setLookAndFeel()
      {
         try
         {
             UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
         }
         catch (Exception exc)
         {
             // ignore error
         }
      }

      public static void main(String args[])
      {
          clockframe clock = new clockframe();
      }

}

Run your code in a debugger, having configured it to break on exceptions: http://stackoverflow.com/questions/3066199/eclipse-break-when-exception-is-thrown — NPE, Aug 10 '13 at 14:55
1) For better help sooner, post an [SSCCE](http://sscce.org/). I'd guess `clockpanel` is actually a frame. But I don't like guessing. 2) Please learn common [Java naming conventions](http://java.sun.com/docs/books/jls/second_edition/html/names.doc.html#73307) (specifically the case used for the names) for class, method & attribute names & use them consistently. — Andrew Thompson, Aug 10 '13 at 15:05

Reimeus · Answer 1 · 2013-08-10T15:18:19.527

2

clockpanel probably extends a window such as JFrame. You probably meant to extend JPanel instead (although doing so is not necessary unless adding new functionality such as custom painting to the new JPanel).

edited Aug 10 '13 at 15:18

answered Aug 10 '13 at 15:07

Reimeus

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score 2 · Answer 2 · answered Aug 10 '13 at 15:08

Take a look at the JFrame documentation

IllegalArgumentException - if index is invalid 
IllegalArgumentException - if adding the container's parent to itself 
IllegalArgumentException - if adding a window to a container

It is looking likely that clockpanel inherits from Window thus triggering the last clause.

Edit: no need to guess any more.. just noticed the top of your stack trace.. this is the cause.

score 0 · Answer 3 · answered Aug 10 '13 at 15:17

0

Answer lies it self in stack trace :

 thread "main" java.lang.IllegalArgumentException adding a window to a container

You are adding window to container, which is not allowed.

answered Aug 10 '13 at 15:17

Alpesh Gediya

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Java unknown exceptions

3 Answers3