• empty file
• missing data field
• extra data field
• invalid data format

import java.awt.*;
import java.applet.*;
import java.util.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
import student.Student;
import student.StudentDB;

public class NewStudentDBTester extends Applet 
                           implements ItemListener,
				      ActionListener { 

  StudentDB studentDB;

  TextArea result,errMessage;
  Button sortButton;

  Choice fileURL;
  Label label1,label2;
  TextField tfNumber;


  String datafile[] = {	"studfile5.html",
			"studfile6.html",
			"studfile7.html",
			"studfile8.html" };
  public void init() {

    sortButton = new Button("Sort by grade");
    result = new TextArea(12,80);
    errMessage = new TextArea("",2,80, TextArea.SCROLLBARS_NONE);
    label1 = new Label("Test Case");
    label2 = new Label("Search by ID");
    tfNumber = new TextField(10);

    fileURL = new Choice();

    for (int i = 0; i < datafile.length; i++)
	fileURL.add(datafile[i]);

    add(label1);
    add(fileURL);
    add(sortButton);
    add(label2);
    add(tfNumber);
    add(result);
    add(errMessage);
     
    fileURL.addItemListener(this);
    tfNumber.addActionListener(this);
    sortButton.addActionListener(this);
  }

  public void itemStateChanged(ItemEvent ie) {

    studentDB = new StudentDB();
    String textLine="",name;
    int number,grade;
    StringTokenizer  st;

    try {
    	URL url = new URL("http://personal.cityu.edu.hk/~dcywchan/2003dco10103/" +
                           fileURL.getSelectedItem());
	URLConnection data = url.openConnection();
        BufferedReader inFile = new BufferedReader(new InputStreamReader(data.getInputStream()));

        try {    
            while((textLine = inFile.readLine()) != null) {
 
               st = new  StringTokenizer(textLine, "_");
               number = Integer.parseInt(st.nextToken());
               name = st.nextToken();
               grade = Integer.parseInt(st.nextToken());

               if (st.hasMoreTokens())  {
                  throw new IllegalArgumentException(textLine);
	       }

   	       studentDB.addStudent(new Student(number,name,grade));
             }
        } catch (NoSuchElementException  nsee)  {
			errMessage.setText(nsee.toString() + " : " + textLine );
        } catch (NumberFormatException  nfe)  {
			errMessage.setText(nfe.toString() + " : " + textLine );
        } catch (IllegalArgumentException iae)  {
			errMessage.setText(iae.toString());
        }

        result.setText("");
        result.setText(studentDB.toString());
        inFile.close();

    } catch(MalformedURLException mue) {}
      catch(IOException ioe) {}
  }

  public void actionPerformed(ActionEvent e) {

    if (e.getSource().equals(sortButton)) {
       studentDB.sortStudentByMark();
       result.setText("");
       result.setText(studentDB.toString());     
    }
    else if (e.getSource().equals(tfNumber)) {
            Student tempStud = new Student(Integer.parseInt(tfNumber.getText()));
            Student lookUpResult = studentDB.lookUpStudent(tempStud);
            if (lookUpResult != null) {
                result.setText("");
                result.setText(lookUpResult.toString());    
            }
         }
  }
}