GUI.java

package com.company;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;


public class GUI extends JFrame
        implements ActionListener {

    int gridX = 10, gridY = 10;

    Plot[][] grid;

    private JPanel panel;

    public void createGUI() {

        setSize(750, 600);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout());

        panel = new JPanel();
        panel.setPreferredSize(new Dimension(300, 200));
        panel.setBackground(Color.white);
        window.add(panel);
        setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {
        Graphics paper = panel.getGraphics();
        paper.drawLine(0, 0, 100, 100);
    }

    private void createGrid() {
        grid = new Plot[gridX][gridY];
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                grid[i][j] = new Plot();
            }
        }
    }


}

Main.java

package com.company;

public class Main {


    public static void main(String[] args) {
        GUI gui = new GUI();
        gui.createGUI();
    }

}

Plot.java

package com.company;

public class Plot {

}