Swing: perform action on main JFrame

Question

Say I have various JFrames open in the same application. Is there a way to perform some action (like update a JTable) when the user changes the focus on one frame to another (like clicking the bar on the top)?

If not is there a way to perform an action on one JFrame when she closes another JFrame?

Answer 1

Please read: The Use of Multiple JFrames, Good/Bad Practice? to see why your program design could very well be improved

As for your main question,

Is there a way to perform some action (like update a JTable) when the user changes the focus on one frame to another (like clicking the bar on the top)?

It's really a specific example of a more general question:

How do I change the state of one object through an event that occurs in another object

and there are several possible solutions

• Easiest would be to have the code that handles the event have a reference to the first object, here one of your JFrames, and simply call a method on it when the event is triggered.
• Better is to structure your program with an MVC (Model-View-Controller) type structure, and in the event code (the control code), change the state of the model. View listeners to the model, including the JFrame you wish to change, would then be notified and would change their appearance based on the model.

Some general recommendations:

• Having a bunch of windows displayed and swapped is very annoying to the user. Have a look at my link above to look for other possible options.
• You'll probably want to avoid having class's extend JFrame, as that forces you to create JFrames with that code. Much better is coding to the JPanel, not the JFrame, and then placing the JPanels created wherever they are needed, be it within a JFrame, or in another JPanel, or swapped via a CardLayout, or in a JTabbedPane, a JDialog, a JOptionPane...