为什么我不能将组件从JFrame中取出？

Question

I have extended the JPanel class with some additional functionality I require, and I then created an instance of it like so:

CustomPanel pan = new CustomPanel();

I then add it to my to my frame:

frame.getContentPane().add(pan);

I then need to the panel back off the frame, I do this like so:

for (Component c : frame.getComponents())
{
    if(c instanceof CustomPanel)
    {
        System.out.println("Should get here");
    }       
}

But it doesn't exist in memory as a CustomPanel, instead it exists as a JPanel, why is this?

Answer 1

From what I understand, the JFrame contains a JPanel, when you add your custom Panel to the JFrame using getContentPane().add(pan), you're actually adding your custom panel to the JFrame's JPanel. I'm guessing you'll have to call frame.getContentPane().getComponents(); to iterate over the components contained in the JFrame's panel.

Answer 2

Your for should read:

for (Component c : frame.getContentPane().getComponents())

You didn't add your Panel to the frame, you added it to the content pane.