How to make a JFrame Modal in Swing java

Your best bet is to use a JDialog instead of a JFrame if you want to make the window modal. Check out details on the introduction of the Modality API in Java 6 for info. There is also a tutorial.

Here is some sample code which will display a JPanel panel in a JDialog which is modal to Frame parentFrame. Except for the constructor, this follows the same pattern as opening a JFrame.

final JDialog frame = new JDialog(parentFrame, frameTitle, true);
frame.getContentPane().add(panel);
frame.pack();
frame.setVisible(true);

Edit: updated Modality API link & added tutorial link (nod to @spork for the bump).

You can create a class that is passed a reference to the parent JFrame and holds it in a JFrame variable. Then you can lock the frame that created your new frame.

parentFrame.disable();

//Some actions

parentFrame.enable();