Leave full-screen mode (Return to normal windowed mode) : Full Screen « 2D Graphics « Java Tutorial

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.Frame;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class Main {
  public static void main(String[] argv) throws Exception {
     GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
     GraphicsDevice gs = ge.getDefaultScreenDevice();

16.47.Full Screen
16.47.1.Full screen mode
16.47.2.Leave full-screen mode (Return to normal windowed mode)
16.47.3.Enter full screen mode
16.47.4.Determine if full-screen mode is supported directly