Why do I have to use setvisible() on my JFrame when I change components?

Question

So for the sake of simplicity I set up a little test code just to figure out this problem. Basically I have a JFrame and I added 'this' to it (I just extended my main class from JComponent to save time). this component fills in a red background. Then I have it sleep for 2 seconds and then type this.

f.remove(this);
thing t = new thing();
f.add(t);
f.setVisible(true);

f being my JFrame object and 'thing' is just another class extending JComponent that paints a blue background..

when I comment out setvisible() it no longer changes to blue.. I've tried using t.setVisible(true) but it seems I have to make the frame visible again, not the component

does anyone know why I have to call that... or if there is another way to change components within a single frame?

Answer 1

"Basically I have a JFrame and I added 'this' to it (I just extended my main class from JComponent to save time). this component fills in a red background. Then I have it sleep for 2 seconds and then type this."

1. Don't "sleep" your program. Instead use a java.swing.Timer to perform repeated tasks on the GUI or for animation. See more at How to Use Swing Timers . You can see a bunch of Timer examples here and here and here and here and here

2. Instead of trying to add and remove panels look into using a CardLayout which allows you to switch between views. It will help you avoid a lot of problems that come with with adding and removing components/containers . See more at How to Use CardLayout . Also see a simple example here .

3. To answer your main question, whenever you remove and add components from your frame, you need to revalidate() it. setVisible() takes care of that for you.

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Side Note

• Seems like a lot adding an removing background panels) just to change the background. Why not just setBackround() ? You can switch colors with the use of the Timer

Answer 2

Calling setVisible(true) makes the frame appear onscreen. Sometimes you might see the show method used instead. The two usages are equivalent, but we use setVisible(true) for consistency's sake.