Java Drawing Lines Example

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

// Creating panel for grid
public class GridPanel extends JPanel
{
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        for(int i = 1; i <=2; i++)
        {
            g.setColor(Color.BLUE);
            g.drawLine(0, i * (getHeight() / 3), getWidth(), i * (getHeight() / 3));
            g.setColor(Color.RED);
            g.drawLine(i * (getWidth() / 3), 0, i * (getWidth() / 3), getHeight());
        }
    }
}