Main.java

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

public class Main {

private static void initAndShow(String filename) {
    JFrame frame = new JFrame("ADS4");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.getContentPane().setPreferredSize(new Dimension(800,600));
    frame.getContentPane().add(new MyCanvas(filename));

    frame.pack();
    frame.setVisible(true);
}

public static void main(String[] args) {
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            initAndShow(args[0]);
        }
    });
}
}

@SuppressWarnings("serial")
class MyCanvas extends JComponent {

String filename;

public MyCanvas(String fname) {
filename = fname;
}

@Override
public void paintComponent(Graphics g) {
if (g instanceof Graphics2D)
{
  Graphics2D g2d = (Graphics2D)g;
  File input = new File(filename);
  try {
  Reader reader = new FileReader(input);
  Lexer lexer = new Lexer(reader);
  LookAhead1 look = new LookAhead1(lexer);
  Parser parser = new Parser(look);
      AST ast=parser.progNotTerm();
      ast.exec(g2d);
      System.out.println("The file is correct");
    }
    catch (Exception e){
      System.out.println("The file is not correct");
      System.out.println(e);
    }
}
}
}