title: How to add support for resizing when using an undecorated JFrame?
body: <p>I would like to customize my titlebar, minimize-, maximize- and the close-button. So I used <code>setUndecorated(true);</code> on my JFrame, but I still want to be able to resize the window. What is the best way to implement that?</p>
  
  <p>I have a border on the RootPane, and I could use MouseListeners on the Border or the RootPane. Any recommendations?</p>
  
  <pre><code>import java.awt.Color;
  
  import javax.swing.JFrame;
  import javax.swing.JMenu;
  import javax.swing.JMenuBar;
  import javax.swing.JMenuItem;
  import javax.swing.border.LineBorder;
  
  public class UndecoratedFrame extends JFrame {
  
      private LineBorder border = new LineBorder(Color.BLUE,2);
      private JMenuBar menuBar = new JMenuBar();
      private JMenu menu = new JMenu("File");
      private JMenuItem item = new JMenuItem("Nothing");
  
      public UndecoratedFrame() {
          menu.add(item);
          menuBar.add(menu);
          this.setJMenuBar(menuBar);
          this.setUndecorated(true);
          this.getRootPane().setBorder(border);
          this.setSize(400,340);
          this.setVisible(true);
      }
  
      public static void main(String[] args) {
          new UndecoratedFrame();
      }
  }
  </code></pre>