Programming Forums > Application Development > Java

GoO · Feb 7th, 2005, 12:17 PM

ok i said this was a n00b program. im still a beginner in this java gui thing...

what's wrong with this program? it says exception in thread "main". java.lang.nullexception... i cant seem to make this work. i checked the syntax, maybe anyone can help? thanks.

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import java.awt.*;

public class ChatClient1 {
	private Frame f1;
	private Panel p1;
	private Button bSend, bQuit, bWhite, bYellow, bBlue;
	private TextArea txtA1;
	private TextField txtF1;
	
	public void ChatClient1() {
		f1 = new Frame("Chat Room");
		p1 = new Panel();
		bSend = new Button("Send");
		bQuit = new Button("Quit");
		bWhite = new Button("White");
		bYellow = new Button("Yellow");
		bBlue = new Button("Blue");
		txtA1 = new TextArea();
		txtF1 = new TextField();
	}
	
	public void launchFrame() {
		f1.add(txtA1, "Center");
		f1.add(txtF1, "South");
		f1.add(p1, "East");
			p1.add(bSend);
			p1.add(bQuit);
			p1.add(bWhite);
			p1.add(bYellow);
			p1.add(bBlue);
		f1.pack();
		f1.setVisible(true);
	}
	
	public static void main(String args[]) {
		ChatClient1 guiWindow = new ChatClient1();
		guiWindow.launchFrame();
	}
}

Dizzutch · Feb 7th, 2005, 1:33 PM

Where are you getting the NullPOinterException? it should give you a line number. When you know that, check all the variables on that line, a NullPointerException gets throws when a variable is accessed that does not point to anything. it points to Null, so make sure all your variables point to something that exists.
good luck
dizz

EdSalamander · Feb 7th, 2005, 1:36 PM

No worries. Take "void" out of your constructor. It (and all constructors you make) should only have visibilty and a name with no return type. It should read..

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public ChatClient1() {
  f1 = new Frame("Chat Room");
  p1 = new Panel();
  etc...
}

The way you have it right now, because it's not a proper constructor, none of those variables are being initialized. When that first add() method is called in launchFrame(), it throws a NullPointerException because the frame f1 doesn't even exist yet (ie, it's still null).

Dizzutch · Feb 7th, 2005, 2:57 PM

ah, i wasn't aware of that. thanks for letting me know that Ed.

EdSalamander · Feb 7th, 2005, 6:57 PM

Just doing my part to save the rainforest.

GoO · Feb 7th, 2005, 10:02 PM

hey thanks a lot! it worked great.

i just saw a sample code from Sun (java student guide) where the constructor is declared void. so i just followed that. anyway thanks again!

Feb 7th, 2005, 12:17 PM	#1
GoO Newbie Join Date: Nov 2004 Posts: 17 Rep Power: 0	n00b gui program help ok i said this was a n00b program. im still a beginner in this java gui thing... what's wrong with this program? it says exception in thread "main". java.lang.nullexception... i cant seem to make this work. i checked the syntax, maybe anyone can help? thanks. (Toggle Plain Text) import java.awt.; public class ChatClient1 { private Frame f1; private Panel p1; private Button bSend, bQuit, bWhite, bYellow, bBlue; private TextArea txtA1; private TextField txtF1; public void ChatClient1() { f1 = new Frame("Chat Room"); p1 = new Panel(); bSend = new Button("Send"); bQuit = new Button("Quit"); bWhite = new Button("White"); bYellow = new Button("Yellow"); bBlue = new Button("Blue"); txtA1 = new TextArea(); txtF1 = new TextField(); } public void launchFrame() { f1.add(txtA1, "Center"); f1.add(txtF1, "South"); f1.add(p1, "East"); p1.add(bSend); p1.add(bQuit); p1.add(bWhite); p1.add(bYellow); p1.add(bBlue); f1.pack(); f1.setVisible(true); } public static void main(String args[]) { ChatClient1 guiWindow = new ChatClient1(); guiWindow.launchFrame(); } } import java.awt.; public class ChatClient1 { private Frame f1; private Panel p1; private Button bSend, bQuit, bWhite, bYellow, bBlue; private TextArea txtA1; private TextField txtF1; public void ChatClient1() { f1 = new Frame("Chat Room"); p1 = new Panel(); bSend = new Button("Send"); bQuit = new Button("Quit"); bWhite = new Button("White"); bYellow = new Button("Yellow"); bBlue = new Button("Blue"); txtA1 = new TextArea(); txtF1 = new TextField(); } public void launchFrame() { f1.add(txtA1, "Center"); f1.add(txtF1, "South"); f1.add(p1, "East"); p1.add(bSend); p1.add(bQuit); p1.add(bWhite); p1.add(bYellow); p1.add(bBlue); f1.pack(); f1.setVisible(true); } public static void main(String args[]) { ChatClient1 guiWindow = new ChatClient1(); guiWindow.launchFrame(); } }

Feb 7th, 2005, 1:33 PM	#2
Dizzutch Professional Programmer Join Date: Dec 2004 Location: Worcester, MA Posts: 441 Rep Power: 4	Where are you getting the NullPOinterException? it should give you a line number. When you know that, check all the variables on that line, a NullPointerException gets throws when a variable is accessed that does not point to anything. it points to Null, so make sure all your variables point to something that exists. good luck dizz __________________ naked pictures of you \| PFO F@H stats

Feb 7th, 2005, 1:36 PM	#3
EdSalamander Programmer Join Date: Dec 2004 Location: Tucson, AZ, USA Posts: 80 Rep Power: 4	No worries. Take "void" out of your constructor. It (and all constructors you make) should only have visibilty and a name with no return type. It should read.. (Toggle Plain Text) public ChatClient1() { f1 = new Frame("Chat Room"); p1 = new Panel(); etc... } public ChatClient1() { f1 = new Frame("Chat Room"); p1 = new Panel(); etc... } The way you have it right now, because it's not a proper constructor, none of those variables are being initialized. When that first add() method is called in launchFrame(), it throws a NullPointerException because the frame f1 doesn't even exist yet (ie, it's still null). __________________ I can pick my friends. And I can pick my nose. So, why can't I pick my friend's nose?

Feb 7th, 2005, 2:57 PM	#4
Dizzutch Professional Programmer Join Date: Dec 2004 Location: Worcester, MA Posts: 441 Rep Power: 4	ah, i wasn't aware of that. thanks for letting me know that Ed. __________________ naked pictures of you \| PFO F@H stats

Feb 7th, 2005, 6:57 PM	#5
EdSalamander Programmer Join Date: Dec 2004 Location: Tucson, AZ, USA Posts: 80 Rep Power: 4	Just doing my part to save the rainforest. __________________ I can pick my friends. And I can pick my nose. So, why can't I pick my friend's nose?

Feb 7th, 2005, 10:02 PM	#6
GoO Newbie Join Date: Nov 2004 Posts: 17 Rep Power: 0	hey thanks a lot! it worked great. i just saw a sample code from Sun (java student guide) where the constructor is declared void. so i just followed that. anyway thanks again!

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Programming Forums > Application Development > Java

n00b gui program help