JFrame Maximize window

Provided that you are extending JFrame:

public void run() {
    MyFrame myFrame = new MyFrame();
    myFrame.setVisible(true);
    myFrame.setExtendedState(myFrame.getExtendedState() | JFrame.MAXIMIZED_BOTH);
}

Something like this.setExtendedState(this.getExtendedState() | this.MAXIMIZED_BOTH);

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

public class Test extends JFrame
{
    public Test()
    {
        GraphicsEnvironment env =
GraphicsEnvironment.getLocalGraphicsEnvironment();
        this.setMaximizedBounds(env.getMaximumWindowBounds());
        this.setExtendedState(this.getExtendedState() | this.MAXIMIZED_BOTH);
    }

    public static void main(String[] args)
    {
        JFrame.setDefaultLookAndFeelDecorated(true);

        Test t = new Test();
        t.setVisible(true);
    }
}

If you're using a JFrame, try this

JFrame frame = new JFrame();
//...
frame.setExtendedState(JFrame.MAXIMIZED_BOTH);

How about JFrame.setExtendedState(JFrame.MAXIMIZED_BOTH)?

The way to set JFrame to full-screen, is to set MAXIMIZED_BOTH option which stands for MAXIMIZED_VERT | MAXIMIZED_HORIZ, which respectively set the frame to maximize vertically and horizontally

package Example;
import java.awt.GraphicsConfiguration;
import javax.swing.JFrame;
import javax.swing.JButton;

public class JFrameExample
{
    static JFrame frame;
    static GraphicsConfiguration gc;
    public static void main(String[] args)
    {
        frame = new JFrame(gc);
        frame.setTitle("Full Screen Example");
        frame.setExtendedState(MAXIMIZED_BOTH);

        JButton button = new JButton("exit");
        b.addActionListener(new ActionListener(){@Override
        public void actionPerformed(ActionEvent arg0){
            JFrameExample.frame.dispose();
            System.exit(0);
        }});

        frame.add(button);
        frame.setVisible(true);
    }
}

I've tried the solutions in this thread and the ones here, but simply calling setExtendedState(getExtendedState()|Frame.MAXIMIZED_BOTH); right after calling setVisible(true); apparently does not work for my environment (Windows 10, JDK 1.8, my taskbar is on the right side of my screen). Doing it this way still leaves a tiny space on the left, right and bottom .

What did work for me however, is calling setExtendedState(... when the window is activated, like so:

public class SomeFrame extends JFrame {

    public SomeFrame() {
        // ...
        setVisible(true);
        setResizable(true);
        // if you are calling setSize() for fallback size, do that here
        addWindowListener (
            new WindowAdapter() {
                private boolean shown = false;
                @Override
                public void windowActivated(WindowEvent we) {
                    if(shown) return;
                    shown = true;
                    setExtendedState(getExtendedState()|JFrame.MAXIMIZED_BOTH);
                }
            }
        );
    }
}

@kgiannakakis answer is fully correct, but if someone stuck into this problem and uses Java 6 on Linux (by example, Mint 19 Cinnamon), MAXIMIZED_BOTH state is sometimes not applied.

You could try to call pack() method after setting this state.

Code example:

public MainFrame() {
    setContentPane(contentPanel); //some JPanel is here
    setPreferredSize(new Dimension(1200, 800));
    setMinimumSize(new Dimension(1200, 800));
    setSize(new Dimension(1200, 800));
    setExtendedState(JFrame.MAXIMIZED_BOTH);
    pack();
}

This is not necessary if you are using Java 7+ or Java 6 on Windows.