I have a java frame that I want to close it automatically after 3 or 4 seconds. I found out I must used threads. but I dont know how exactly to do it, this a dumy part of my code :

package intro;

import java.awt.*;
import java.io.IOException;
//import view.LangMenu;

public class IntroClass extends Frame {

    private int _screenWidth = 0;
    private int _screenHeight = 0;
    private int _screenCenterx = 0;
    private int _screenCentery = 0;

    //private static final String SOUND_PATH="/sounds/introSound.midi";
    public IntroClass() {
        Toolkit thisScreen = Toolkit.getDefaultToolkit();
        Dimension thisScrrensize = thisScreen.getScreenSize();

        _screenWidth = thisScrrensize.width;
        _screenHeight = thisScrrensize.height;
        _screenCenterx = _screenWidth / 2;
        _screenCentery = _screenHeight / 2;
        setBackground(Color.pink);
        Label lbl = new Label("Welcome To Dots Game. Samaneh Khaleghi", Label.CENTER);
        add(lbl);
        setUndecorated(true);
        setLocation((_screenCenterx*50)/100,_screenCentery-(_screenCentery*50)/100);
        setSize((_screenWidth * 50) / 100, (_screenHeight * 50) / 100);

        WaitClass r = new WaitClass();
        r.start();
        view.DotsBoardFrame d=new view.DotsBoardFrame();
                main.Main.showScreen(d);
    }

    class WaitClass extends Thread {

        boolean running = true;

        public void run() {
            while (running) {
                try {
                    Thread.sleep(50);
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }                
            }
        }
    }
}