How to set width of specific panel with BoxLayout Manager

Question

The code below places 3 JPanels inside a JFrame. I want the blue colored panel to have a width of 300 (assume the enclosing Frame has a width of greater than 300). The width of the other two panels should be the remainder. How do I do that?

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;

import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PanelTest extends JFrame { 
    private JPanel leftpanel;

    public PanelTest() {
        getContentPane().setLayout(new BoxLayout(this.getContentPane(), BoxLayout.X_AXIS));
        this.leftpanel = new JPanel() {         
            @Override
            public Dimension getMaximumSize() {
                return new Dimension(300, 9999);
            }
            
            @Override
            public Dimension getMinimumSize() {
                return new Dimension(300, 0);
            }   
        };
        this.leftpanel.setBackground(Color.blue);
        getContentPane().add(leftpanel);

        JPanel rightpanel = new JPanel();
        getContentPane().add(rightpanel);
        rightpanel.setLayout(new BoxLayout(rightpanel, BoxLayout.Y_AXIS));
        
        JPanel upperpanel = new JPanel();
        upperpanel.setBackground(Color.red);
        rightpanel.add(upperpanel);
        
        JPanel lowerpanel = new JPanel();
        lowerpanel.setBackground(Color.yellow);
        rightpanel.add(lowerpanel);
        pack();
        setVisible(true);
        setExtendedState(Frame.MAXIMIZED_BOTH);
    }
    
    public static void main(String[] args) {
        new PanelTest();
    }
}

I slightly updated the above code using @camickr's suggestion of using BorderLayout. The width is now as desired. Thanks @camickr.

I still think BoxLayout should have respected the minimum and maximum sizes. Taking those into consideration, it should have set the width to 500.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;

import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class PanelTest extends JFrame { 
    public PanelTest() {
        getContentPane().setLayout(new BorderLayout());
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel leftpanel = new JPanel();
        int width = 500;
        leftpanel.setPreferredSize(new Dimension(width, 1));
        leftpanel.setBackground(Color.blue);
        getContentPane().add(leftpanel, BorderLayout.LINE_START);

        JPanel rightpanel = new JPanel();
        getContentPane().add(rightpanel, BorderLayout.CENTER);
        rightpanel.setLayout(new BoxLayout(rightpanel, BoxLayout.Y_AXIS));
        
        JPanel upperpanel = new JPanel();
        upperpanel.setBackground(Color.red);
        rightpanel.add(upperpanel);
        
        JPanel lowerpanel = new JPanel();
        lowerpanel.setBackground(Color.yellow);
        rightpanel.add(lowerpanel);
        pack();
        setVisible(true);
        setExtendedState(Frame.MAXIMIZED_BOTH);
    }
    
    public static void main(String[] args) {
        new PanelTest();
    }
}