[Java] Swing -- Closes immediately after opened

[dt]

Hi all,

Something strange is up with my app.

It's only two classes thus far. One has the bulk of the code and the other has a main method, which instantiates an object of type (the other class). In doing so, the constructor of the other class does appropriate operations as I'd like and then calls upon the display method.. but after it does that, the java swing window (JFrame) instantly closes.

Any ideas?

Here's the method that's supposed to do the displaying. it's not really what it's supposed to end up doing, but ... you get the idea (I hope) :p

 // (javax.swing.* was imported at the top of the class)
public void displayStats()
	{
		JFrame.setDefaultLookAndFeelDecorated(true);
		JFrame fr = new JFrame("Statistician - Results");

		fr.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
		JLabel label = new JLabel("hiiiii");
		JComponent comp = new JTextArea();
		fr.getContentPane().add(label);
		fr.getContentPane().add(comp, 100);

		fr.setSize(100,300);
		fr.pack();
		fr.setVisible(true);
	}

Thanks,,

--dt

[kjordan2001]

Well, I get an illegal component position on your add(comp,100); line, so maybe that's what's causing your window to close?

[dt]

well I used that because it wouldn't accept BorderLayout.CENTER for some reason...

O_o

However it compiles for me..

I use Eclipse BTW

Thanks

[kjordan2001]

  dt said:

well I used that because it wouldn't accept BorderLayout.CENTER for some reason...

O_o

However it compiles for me..

I use Eclipse BTW

Thanks

Well, it compiles for me too, but when I go to run it, I get that runtime exception.

[Wheazel]

you forgot the specify the layout manager

frame.setLayout(new BorderLayout());

[dt]

  Wheazel said:

you forgot the specify the layout manager

frame.setLayout(new BorderLayout());

That didn't help; it still closes immediately. :(

Here's what I've got so far.

(java.awt.BorderLayout and javax.swing.* are both imported at the top of the class)

	public void displayStats()
	{
		JFrame.setDefaultLookAndFeelDecorated(true);
		JFrame fr = new JFrame("Statistician - Results");
		fr.setLayout(new BorderLayout());
		fr.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
		JLabel label = new JLabel("hiiiii");
		JComponent comp = new JTextArea();
		fr.getContentPane().add(label);
		fr.getContentPane().add(comp, BorderLayout.CENTER);

		fr.setSize(100,300);
		fr.pack();
		fr.setVisible(true);
	}

Thanks,

dt

edit: Does it matter that I'm calling displayStats() from the class's constructor? Also, does it matter that the class whose main method instantiates an object of type (this class, which contains displayStats()) does not import swing?

[DJ Trauma]

Hmm, it compiles and runs perfect for me (in netbeans 5.0).

Did you import java.awt.* at the top of the class?

[dt]

  DJ Trauma said:

Hmm, it compiles and runs perfect for me (in netbeans 5.0).

Did you import java.awt.* at the top of the class?

Which class?

Upon doing that in the class with the method whose code I displayed above, the same problem occurred.

:/ Thanks anyway though..

[dt]

Update. I made an observation. When I comment out the constructor, the JFrame pops up just fine. It's something in the constructor apparently, that breaks swing :(

public StatsCalc()
	{
		try {
			numItems = Integer.valueOf(JOptionPane.showInputDialog
					("How many items?"));
			data = new double[numItems];

			for (int i = 0; i < numItems; i++)
			{
				String st = JOptionPane.showInputDialog(
						"Enter item #" + (i+1) + ":");
				if (st == "")
					numItems--;
				else
					data[i] = Double.valueOf(st);
				if (st == null)
					throw new java.lang.NumberFormatException();
			}			
		} catch (java.lang.NumberFormatException e) {
			System.err.println("Invalide.");
		} finally {
			System.exit(0); 
		}
	}

I'm a noob at exceptions so if that has some kind of error could you kindly point it out? :) Please and thanks lol.

EDIT: I removed the exception handling and now it works without problems.

Why, though? Why can't I use exception handling AND swing like this? :confused:

Edited April 10, 2006 by dt

[kjordan2001]

You sure you want that finally { System.exit(0); }? It will execute no matter what happens and will terminate your program.

[scottb]

  dt said:

Does it matter that I'm calling displayStats() from the class's constructor? Also, does it matter that the class whose main method instantiates an object of type (this class, which contains displayStats()) does not import swing?

erm i belive constructors are there to inialize variables not to call methods, however i have called the thread start method in a constructor b4, like thrd.start(). if your main method is in its own class which it should be (thats what i do), then it should matter... but only if you are putitng classes in seperate files e.g class1.java, class2.java but if they are all in one file then it shoudltn matter.

  kjordan2001 said:

You sure you want that finally { System.exit(0); }? It will execute no matter what happens and will terminate your program.

yeh i agree... i was thinking when i first started reading this i bet he has got a system.exit(0) in there somewhere, and its just recahing it and terminating.

hope that makes sense.

[dt]

Ohhh ok. Thanks for the help :)

I have a question then; how do I define what the app does after catching a certain type of exception? Is "finally" simply unnecessary then?

Also, with regards to swing, if I'd like to popup a JFrame with several JLabels, they seem to overlap one another so that only the last one initialized appears. How do I make them appear on different lines? Looking around online yielded some stuff about "BorderLayout"s and the like, but I don't really understand how they have to do with JFrames or how they can work together to arrange / position the components (e.g. JPanel or JLabel) in the JFrame. Can anyone direct me to some kind of comprehensive guide or something that can help me get this concept? Thanks a lot! :yes:

[kjordan2001]

  dt said:

Ohhh ok. Thanks for the help :)

I have a question then; how do I define what the app does after catching a certain type of exception? Is "finally" simply unnecessary then?

Also, with regards to swing, if I'd like to popup a JFrame with several JLabels, they seem to overlap one another so that only the last one initialized appears. How do I make them appear on different lines? Looking around online yielded some stuff about "BorderLayout"s and the like, but I don't really understand how they have to do with JFrames or how they can work together to arrange / position the components (e.g. JPanel or JLabel) in the JFrame. Can anyone direct me to some kind of comprehensive guide or something that can help me get this concept? Thanks a lot! :yes:

The finally block is mainly for cleanup. Say you wanted to close a file or something no matter what happened, you would put that in the finally block, otherwise you're likely to duplicate code (i.e. having a close in the try and a close in the catch).

JFrames don't handle the layout of the components. That's why you need to specify a layout type. The default layout if none is specified is a FlowLayout. This basically puts components on the same line until it can't fit any more and then puts the newest ones on the next line.

On the other hand, BorderLayout does it by putting a component in either N, S, E, W, or the center direction of the Frame. If you want to put one under another or next to each other, you might consider GridLayout.