Saving JPanel Graphics

I'm not quite sure exactly how Graphics work in Java so I having trouble debugging my problem. I have a Class MyFrame Extends JPanel. Now I do some drawing on MyFrame save and save me properties about that certain frame then add it an ArrayList collection of MyFrames. Later on I want to recall the properties a certain instance of MyFrame and repaint that frame on the screen. Having the the graphic of frame show up again is what I am having trouble with.

Here is a quick bit of code that will demonstrate my problem.

public class MyFrame extends JPanel{
private int property;
private int x;
private int y;

public MyFrame(int xp, int yp){
x = xp;
y = yp;
}

@override
public void paintComponent(Graphics g){
super.paintComponent(g);
g.fillRect(x,y,5,5);
}
public void setProperty(int p){
property = 开发者_高级运维p;
}
}

public class MainClass() extends JPanel{
private ArrayList<MyFrame> frames = new ArrayList<MyFrame>;
private MyFrame currentFrame = new MyFrame();

public void addFrame(int x, int y){
this.remove(currentFrame);
currentFrame = new MyFrame();
this.add(currentFrame);
frames.add(currentFrame);
}

public void setFrame(int frame){
this.remove(currentFrame);
currentFrame = frames.get(frame);
this.add(currentFrame);
}

}

Summary: I'd like the panel to display the correct frame when setFrame is called. currently when I do this set frame will be blank.

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You seem to be swapping JPanels in and out of another JPanel, and when doing this, you must take into consideration the layout used by the container-JPanel and you would need to call revalidate and repaint on the container-JPanel after the swap.

But rather than mess with all of this, why not go the easy route by just swaping JPanels or perhaps JLabels with ImageIcons holding an image using a CardLayout?

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You could also consider adding some states, an enum data member, to a single JPanel and ask it to switch from one state to another, then call its repaint method and, in its paintComponent overriden method, draw some graphics according to its state.

Your architecture (as enhance by @Hovercraft Full of Eels is also good, even better if the draw methods vary quite a lot and have very different purposes. However, my proposal could lay to a faster app, and could allow other fatures such as transition between states, shared double buffer, variable/code reuse in case graphics are close.

What is your app doing ?

Regards, Stéphane