kami's hideout Gavrilov V. Miroslav

Checkboxes in listboxes in Java(boxes)

I vote the swing implementation of the ListBox as the most complicated model out there. It is pretty general and useful, it's just that minor modifications turn into some very excessive work and the net is full of useful-as-an-example-but-not-an-implementation tutorials of how to ruin good object-oriented code. The main problem with this is having programmers who think in other paradigms write object-oriented code. Then you end up with a class that embeds the main() method and does all the modifications to the JList, and actually is a JFrame. I've turned the code from codeguru.com - that exhibits this trait - into a class, the CheckListBox and it works out of the box, and extends JList, so that you could do things with it that you could do with an ordinary list. Here's a couple of screenshots; it has a scrollpane in itself, as demonstrated in the second one.
The download begins here.

To setup the CheckListBox, let's make a Test class:

public class Test extends JFrame {
	public static void main(String[] args) {
		new Test();
	}

	public Test() {
	}
}

Let's first import the component (if you've downloaded the .jar file, you also have to include it in your class path).

import kami.begaj.net.checklist.CheckListBox;

Next up, let's initialize the JFrame...

	public Test() {
		try {
			UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
		} catch (Exception e) {
			System.out.println("Unable to find System Look and Feel");
		}

		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setSize(350, 200);
		setVisible(true);
	}

Now, let's create the data list for our check list - the example on codeguru.com used fruits, so let's follow...

		String[] listData = { "Apple", "Orange", "Cherry", "Blue Berry",
				"Banana", "Red Plum", "Watermelon" };

Lastly, before setting up the frame, let's create the CheckListBox with the data given in this array:

		CheckListBox check = new CheckListBox(listData);

The most important part of the whole thing is to remember to add it to the form using the .setup() method, instead of the containers .add() method.

		// unless you're doing something extravagant...
		check.setup(this.getContentPane());

Why do we do this like this? For the implementation to be versatile enough, a ScrollPane has been added to it, so that the user could skip this part and just use the list. Using the .add() method actually adds the JList-extended CheckBoxList to the frame, not the ScrollPane. The .setup() method takes care of this. Also, if anyone extends the CheckBoxList, he would just redefine this .setup() method to meet his implementational needs.
The full grown code for our test example is now:

import javax.swing.JFrame;
import javax.swing.UIManager;

import kami.begaj.net.checklist.CheckListBox;

public class Test extends JFrame {
	public static void main(String[] args) {
		new Test();
	}

	public Test() {
		String[] listData = { "Apple", "Orange", "Cherry", "Blue Berry",
				"Banana", "Red Plum", "Watermelon" };

		try {
			UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
		} catch (Exception e) {
			System.out.println("Unable to find System Look and Feel");
		}

		CheckListBox check = new CheckListBox(listData);
		check.setup(this.getContentPane());		

		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		setSize(350, 200);
		setVisible(true);
	}
}

The results are on the pictures above. Sun should really think about remodeling the UI packages for more comfort. As asked, here's the code of the CheckBoxList class packed in one .java file instead of a .jar.. The code is below, but for what it's worth, we could also skip showing it on the blog homepage, as it's quite longer than the previous cuts..