最大化窗口

If you're using a JFrame, try this

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

How about JFrame.setExtendedState(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);
}
}

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);
}
}

Provided that you are extending JFrame:

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

i like this version:

import java.awt.Dimension;
import java.awt.GraphicsConfiguration;
import java.awt.Toolkit;
import javax.swing.JFrame;


public class Test
{
public static void main(String [] args)
{
final JFrame frame = new JFrame();
final GraphicsConfiguration config = frame.getGraphicsConfiguration();


final int left = Toolkit.getDefaultToolkit().getScreenInsets(config).left;
final int right = Toolkit.getDefaultToolkit().getScreenInsets(config).right;
final int top = Toolkit.getDefaultToolkit().getScreenInsets(config).top;
final int bottom = Toolkit.getDefaultToolkit().getScreenInsets(config).bottom;


final Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
final int width = screenSize.width - left - right;
final int height = screenSize.height - top - bottom;


frame.setResizable(false);
frame.setSize(width,height);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}

I ended up using this code:

public void setMaximized(boolean maximized){
if(maximized){
DisplayMode mode = this.getGraphicsConfiguration().getDevice().getDisplayMode();
Insets insets = Toolkit.getDefaultToolkit().getScreenInsets(this.getGraphicsConfiguration());
this.setMaximizedBounds(new Rectangle(
mode.getWidth() - insets.right - insets.left,
mode.getHeight() - insets.top - insets.bottom
));
this.setExtendedState(this.getExtendedState() | JFrame.MAXIMIZED_BOTH);
}else{
this.setExtendedState(JFrame.NORMAL);
}
}

This options worked the best of all the options, including multiple monitor support. The only flaw this has is that the taskbar offset is used on all monitors is some configurations.

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.