How to maximize undecorated java swing screen?

Question

how the screen looks

I would like to know how do I make the screen maximized in the undecorated Jframe, because with the undecorated false it maximizes normally, but with the undecorated true the jframe looks like this.

private void jlMaximizarMenuMouseClicked(java.awt.event.MouseEvent evt) {                                             
        if (this.getExtendedState() != Menu.MAXIMIZED_BOTH) 
        {
          this.setExtendedState(Menu.MAXIMIZED_BOTH);
        }
        else
        {
            this.setExtendedState(Menu.NORMAL);
        }
    }  

Answer 1

This simple example works perfectly fine, your issue is some where else in code you are not sharing. I'm guessing you're using a transparent window, which suggests that either you're not using one or more appropriate layouts or you're otherwise screwing with the layout information, in any case, without a minimal reproducible example, there's not much more we can do to help you.

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Main {
    public static void main(String[] args) {
        new Main();
    }

    public Main() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.setUndecorated(true);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            JButton normal = new JButton("Normal");
            JButton maximized = new JButton("Maximixed");
            JButton minimized = new JButton("Minimized");

            add(normal);
            add(maximized);
            add(minimized);

            normal.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    ((JFrame)SwingUtilities.windowForComponent(TestPane.this)).setExtendedState(JFrame.NORMAL);
                }
            });
            maximized.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    ((JFrame)SwingUtilities.windowForComponent(TestPane.this)).setExtendedState(JFrame.MAXIMIZED_BOTH);
                }
            });
            minimized.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    ((JFrame)SwingUtilities.windowForComponent(TestPane.this)).setExtendedState(JFrame.ICONIFIED);
                }
            });
        }

    }
}