Screen.java

package core;
import java.awt.*;
import javax.swing.JFrame;

public class Screen {
    private GraphicsDevice vc;

    public Screen(){
        GraphicsEnvironment env = GraphicsEnvironment.getLocalGraphicsEnvironment();
        vc = env.getDefaultScreenDevice();
    }

    public void setScreenSize(DisplayMode dm, JFrame window) {
        window.setUndecorated(false);
        window.setResizable(false);
        window.setSize(800, 600);

        if (dm !=null && vc.isDisplayChangeSupported()){
            try{
                vc.setDisplayMode(dm);

            }catch(Exception ex){
            }
        }
    }
    public Window getWindow(){
        return vc.getFullScreenWindow();
    }
    public void RestoreScreen(){
        Window w = vc.getFullScreenWindow();
        if(w != null){
            w.dispose();
        }
        vc.setFullScreenWindow(null);
    }
}