while trying to create a panel for my game, I am trying to use a number of things such as setPreferredSize, setBackground, and more, but for some reason all of these are being underlined. Also, I’m following this video: https://www.youtube.com/watch?v=om59cwR7psI&t=702s and I have been following the steps very closely so I’m not sure why it isn’t working for me.

package main;
import java.awt.*; 
import javax.swing.*; 
import java.awt.Color;
import java.awt.Dimension;

public class GamePanel {
    final int originalTileSize = 16; //16 x 16 tiles 
    final int scale = 3; 

    final int tileSize = originalTileSize * scale; 
    final int maxScreenColumn = 16; 
    final int maxScreenRow = 12; 
    final int screenWidth = tileSize * maxScreenColumn; //768 pixels
    final int screenHeight = tileSize * maxScreenRow; //576 pixels  

    public GamePanel() { 
        this.setPreferredSize(new Dimension(screenWidth, screenHeight)); 
        this.setBackground(Color.black);
        this.setDoubleBuffered(true); 
    }

}