How to move an undecorated JFrame?

The following example illustrates how to move an undecorated JFrame. As they don't move by default, we need to keep a component that acts like a titlebar, add a MouseListener and MouseMotionListener for it to listen to mousePressed and mouseDragged respectively and change the location accordingly. The logic  is going to be dead simple. And in this program, I'll be using a JMenuBar with the three buttons that act as minimize, maximize, close buttons. In this example, you'll learn:

1. How to remove titlebar in JFrame?
2. How to set JMenuBar as custom title bar and add buttons to it?
3. How to minimize a JFrame and full screen it?
4. How to set a custom look and feel?
5. How to set fonts?
6. How to set JFrame location and make it appear at center?
7. How to set a rounded rectangle shape for JFrame?

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class CustomTitlebar extends JFrame
{
JPanel p;
JMenuBar mb;
JButton close,min,max;
Font f=new Font("Arial",Font.BOLD,24);
int pX,pY;

    public CustomTitlebar()
    {
        createAndShowGUI();
    }
    
    private void createAndShowGUI()
    {
        // Custom look and feel
        try
        {
            UIManager.setLookAndFeel("javax.swing.plaf.nimbus.NimbusLookAndFeel");
        }catch(Exception e){}
        
        setTitle("Custom Titlebar");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setUndecorated(true);        
        
        // Create JMenuBar
        mb=new JMenuBar();
        mb.setLayout(new BorderLayout());
        
        // Create panel
        p=new JPanel();
        p.setOpaque(false);
        p.setLayout(new GridLayout(1,3));
        
        // Create buttons
        min=new JButton("-");
        max=new JButton("+");
        close=new JButton("x");
        
        min.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent ae)
            {
                // minimize
                setState(ICONIFIED);
            }
        });
        
        max.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent ae)
            {
                maximize();
            }
        });
        
        close.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent ae)
            {
                // terminate program
                System.exit(0);
            }
        });
        
        // set focus painted false
        // i don't like it, so i removed it
        // if you like, you can remove these steps
        min.setFocusPainted(false);
        max.setFocusPainted(false);
        close.setFocusPainted(false);
        
        // font, again if you don't like you can
        // remove these steps, also remove the Font object
        min.setFont(f);
        max.setFont(f);
        close.setFont(f);
        
        // Add buttons
        p.add(close);
        p.add(max);
        p.add(min);
        
        // To west, mac style!
        mb.add(p,BorderLayout.WEST);
        
        // Add mouse listener for JMenuBar mb
        mb.addMouseListener(new MouseAdapter(){
            public void mousePressed(MouseEvent me)
            {
                // Get x,y and store them
                pX=me.getX();
                pY=me.getY();
            }
        });
        
        // Add MouseMotionListener for detecting drag
        mb.addMouseMotionListener(new MouseAdapter(){
            public void mouseDragged(MouseEvent me)
            {
                // Set the location
                // get the current location x-co-ordinate and then get
                // the current drag x co-ordinate, add them and subtract most recent
                // mouse pressed x co-ordinate
                // do same for y co-ordinate
                setLocation(getLocation().x+me.getX()-pX,getLocation().y+me.getY()-pY);
            }
        });
        
        // Set the menu bar
        setJMenuBar(mb);
        
        // Set size, visibility,shape and center it
        setSize(400,400);
        setVisible(true);
        setShape(new java.awt.geom.RoundRectangle2D.Double(0,0,getWidth(),getHeight(),5,5));
        setLocationRelativeTo(null);
    }
    
    private void maximize()
    {
    // Get GraphicsEnvironment object for getting GraphicsDevice object
    GraphicsEnvironment env=GraphicsEnvironment.getLocalGraphicsEnvironment();
    
    // Get the screen devices
    GraphicsDevice[] g=env.getScreenDevices();
    
    // I only have one, the first one
    // If current window is full screen, set fullscreen window to null
    // else set the current screen
    g[0].setFullScreenWindow(g[0].getFullScreenWindow()==this?null:this);
    }
    
    public static void main(String args[])
    {
        new CustomTitlebar();
    }
}

In this way we can set a custom JMenuBar and make it act like the title bar by adding buttons to it. Next, using the MouseListener we can move the JFrame though it is undecorated.