Question

I’ve been staring at my code for hours, and I’ve cut out almost everything down to the simplest bits and I don’t know how to make a JPanel expand to the size of the frame. Ideally (in the end) I’d like a container panel with a north and south content panels. The north panel needs to take up whatever space is leftover once the south panel is placed.

For now, though, I have a tiny red speck that is only as big as its content. Can someone give me some insight into what I am doing fundamentally wrong?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;

public class TestCode extends JFrame {

    private DescriptionPanel window = new DescriptionPanel();

    public static void main(String[] args){
     TestCode frame = new TestCode();
     frame.pack();
     frame.setTitle("Grape Project");
     frame.setLocationRelativeTo(null);
     frame.setSize(400, 300);
     frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
     frame.setVisible(true);
    }

    public TestCode(){
        add(window);
    }
}

And the DescriptionPanel class:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class DescriptionPanel extends JPanel{

    private JPanel container = new JPanel();

    public DescriptionPanel(ImageIcon pic, JLabel text){

        container.setBackground(Color.red);
        add(container);
    }
}

Answer 1

This is a typical BorderLayout scenario.

By default, JPanels have a FlowLayout already set, so you need to call setLayout, or you can initialize your DescriptionPanel with the proper layout manager :

super(new BorderLayout()); 
// setLayout(new BorderLayout());

add(top,    BorderLayout.CENTER);  // take all available upper space left
add(bottom, BorderLayout.SOUTH);   // take the vertical space specified