Test.txt

import javax.swing.JFrame;
import javax.swing.JPanel;
import java.awt.Graphics;

public class Test {
    public static void main(String[] args) {
        GameWindow gw = new GameWindow("Life Game", 400, 300);
        gw.add(new DrawCanvas());// 描画領域の追加
        gw.setVisible(true);
        LifeGame l = new LifeGame();
        System.out.println(l.toString());
    }
}

// ウィンドウクラス
class GameWindow extends JFrame {
    private static final long serialVersionUID = 1L;

    public GameWindow(String title, int width, int height) {
        super(title);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(width, height);
        setLocationRelativeTo(null);
        setResizable(false);
    }
}

// 描画する紙を表すクラス
class DrawCanvas extends JPanel {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.fillRect(200, 100, 50, 50); // 矩形の塗りつぶし
    }
}