Java Swing question

Factual Questions
1

I’m creating a prototype user interface for a program, which currently contains a menubar, a JPanel, and a JTextArea.

When I run it, all that gets displayed is the Text Area but not the JPanel with all the labels.

Originally I was using ImageIcons for the labels, but for debugging purposes I changed to using text only labels, and commented out the image icons being created.

I am using pack, and set visible and I’ve tried validate. This isn’t an applet just an application. Anyone got any idea why my JPanel isn’t showing up?

…
paintPanel = new JPanel(new GridLayout(20, 20));

// populate the grid with dummy icons until full implementation is underway
   // then the JPanel will be filled from Simulation

/* ImageIcon icon1 = new ImageIcon("~/documents/source/politician.jpg");
ImageIcon icon2 = new ImageIcon("~/documents/source/lobbyist.jpg");
ImageIcon icon3 = new ImageIcon("~/documents/source/dollar.jpg");*/

for(int i = 0; i < 20; i++)
{
	for(int j = 0; j < 20; j++)
	{
		if((20 * i + j) % 6 == 0)
			paintPanel.add(new JLabel("A"));
		else if((20 * i + j) % 6 == 1)
			paintPanel.add(new JLabel("B"));
		else if((20 * i + j) % 6 == 2)
			paintPanel.add(new JLabel("C"));
		else
			paintPanel.add(new JLabel(" "));
	}
}
	
paintPanel.validate();
paintScroll = new JScrollPane(paintPanel);
frame.getContentPane().add(paintScroll);
	
log = new JTextArea("Political Predator Prey System

A group two production.");
textScroll = new JScrollPane(log);
frame.getContentPane().add(textScroll);
…

2

I figured it out. The default layout for a content pane of a JFrame must be bad or something. Finally I figured out that I needed to set that layout as well as the JPanel layout and everything finally showed up on the screen.

Like all bugs there is a :smack: :smack: :smack: moment at how simple it is in the end.

3

You got it. Just so you don’t wonder what the “must be bad or something” part of the problem is, here goes:

First your code:



paintPanel.validate();
paintScroll = new JScrollPane(paintPanel);
frame.getContentPane().add(paintScroll);

log = new JTextArea("Political Predator Prey System
A group two production.");
textScroll = new JScrollPane(log);
frame.getContentPane().add(textScroll);

You have called “add” on the JFrame’s content pane twice with no constraints.

The default layout manager of a JFrame is BorderLayout.

From the JDK docs on BorderLayout:

Hence, you have added one component to CENTER, followed by adding another component to CENTER. In essence, you have overwritten paintScroll with textScroll.