(java.lang.IllegalArgumentException) Error with gui -

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i making simple gui program in java. when click run gives me error looks this:

exception in thread "awt-eventqueue-0" java.lang.illegalargumentexception: adding window container @ java.awt.container.checknotawindow(unknown source) @ java.awt.container.addimpl(unknown source) @ javax.swing.jlayeredpane.addimpl(unknown source) @ java.awt.container.add(unknown source) @ javax.swing.jrootpane.setcontentpane(unknown source) @ javax.swing.jframe.setcontentpane(unknown source) @ main.cool(main.java:31) @ main$1.run(main.java:43) @ java.awt.event.invocationevent.dispatch(unknown source) @ java.awt.eventqueue.dispatcheventimpl(unknown source) @ java.awt.eventqueue.access$500(unknown source) @ java.awt.eventqueue$3.run(unknown source) @ java.awt.eventqueue$3.run(unknown source) @ java.security.accesscontroller.doprivileged(native method) @ java.security.protectiondomain$javasecurityaccessimpl.dointersectionprivilege(unknown source) @ java.awt.eventqueue.dispatchevent(unknown source) @ java.awt.eventdispatchthread.pumponeeventforfilters(unknown source) @ java.awt.eventdispatchthread.pumpeventsforfilter(unknown source) @ java.awt.eventdispatchthread.pumpeventsforhierarchy(unknown source) @ java.awt.eventdispatchthread.pumpevents(unknown source) @ java.awt.eventdispatchthread.pumpevents(unknown source) @ java.awt.eventdispatchthread.run(unknown source)

and here code:

import javax.swing.*;  import java.awt.container; import java.awt.event.*;    public class main extends jframe implements actionlistener {  protected jbutton click, fun;  public main() {     click = new jbutton("click");     click.setactioncommand("click");     click.addactionlistener(this);     add(click);     click.setsize(16, 16);     fun = new jbutton("wow");     fun.setactioncommand("wow");     fun.addactionlistener(this);     add(fun);  }  public static void cool() {     jframe frame = new jframe("test!");     frame.setdefaultcloseoperation(jframe.exit_on_close);     main main = new main();     frame.setcontentpane(main);     frame.setsize(128, 128);     frame.setvisible(true);     frame.setresizable(true); }   public static void main(string[] args) {     javax.swing.swingutilities.invokelater(new runnable() {          public void run()         {             cool();         }     });  }      public void actionperformed(actionevent e) {     // todo auto-generated method stub     if("click".equals(e.getactioncommand()))     {         system.out.println("oh right");     } else if ("wow".equals(e.getactioncommand()))     {         system.out.println("hi");     } }  }

i believe bug may in cool() method; setcontentpane line. not sure. can please me.

yes; bug triggered in frame.setcontentpanel() in cool() method in main class. main class should extend jpanel instead of extend jframe.

aside: avoid declaring local variables match class names; and, avoid declaring class names same standard method names...so, rename main class main (if must, try more descriptive...perhaps application), , make local variable name other main...perhaps m or application.


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