• only one student
• repeated student
• 6 students
• typical class
• 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.StudentFormatException;

public class VectorStudentDBTester extends Applet 
                           implements ItemListener,
				      ActionListener { 

  Vector studentDB;

  TextArea result,errMessage;
  Button sortButton;

  Choice fileURL;
  Label label1,label2;
  TextField tfNumber;


  String datafile[] = {	"studfile1.html",
			"studfile2.html",
			"studfile3.html",
			"studfile4.html",
			"studfile5.html",
			"studfile6.html",
			"studfile7.html",
			"studfile8.html" };
  public void init() {

    sortButton = new Button("Sort by Number");
    result = new TextArea(12,80);
    errMessage = new TextArea(4,80);
    label1 = new Label("Test Case");
    label2 = new Label("Search Grade #");
    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 Vector();
    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();
        Reader inFile = new InputStreamReader(data.getInputStream());

	studentDB = makeVectorFromReader(inFile,"_");

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

    } catch(StudentFormatException se) {
            errMessage.setText("");
            errMessage.setText(se.toString());
    }
      catch(MalformedURLException mue) {}
      catch(IOException ioe) {}
  }

  public void actionPerformed(ActionEvent e) {

    if (e.getSource().equals(sortButton)) {

       int[] arr = getNumbers(studentDB);
       String s = "";

       result.setText("");

       for (int i = 0; i < arr.length; i++)
            s = s+arr[i]+'\n';

       result.setText(s);     
    }
    else if (e.getSource().equals(tfNumber)) {

            int grade = Integer.parseInt(tfNumber.getText());
            int lookUpResult = countGradeGreaterOEqual(studentDB,grade);

            result.setText("");
            result.setText("Number of student with Grade >= " + grade + " is " + lookUpResult);    
            
         }
  }

      public static int countGradeGreaterOEqual(Vector vector, int n)  {
		
		int  count = 0;

		for (Iterator  i = vector.iterator(); i.hasNext(); ) {
			if (((Student) i.next()).getGrade() >= n) {
				count++;
			}
		}

		return count;
	}

       public static int[] getNumbers(Vector  vector)  {
		
		int  nums[] = new int[vector.size()];
		int  i = 0;
		
		for (Iterator  it = vector.iterator() ; it.hasNext();)  {
			nums[i++] = ((Student) it.next()).getNumber();
		}
		Arrays.sort(nums);

		return nums;
	}

 	public static Vector makeVectorFromReader(Reader  r, final String  DELIM)
			throws IOException, StudentFormatException {
		
		BufferedReader br = new  BufferedReader(r);
		Vector  v = new  Vector();
		
		StringTokenizer  st;
		String  line = "";
		
		int  number;
		String  name;
		int  grade;
		
		try {		
			line = br.readLine();
			while (line != null)  {
				st = new  StringTokenizer(line, DELIM);
				number = Integer.parseInt(st.nextToken());
				name = st.nextToken();
				grade = Integer.parseInt(st.nextToken());

				if (st.hasMoreTokens())  {
						throw  new  StudentFormatException(line);
				}

				v.add(new  Student(number, name, grade));
				line = br.readLine();
			}
		} catch (NoSuchElementException  nsee)  {
			throw  new  StudentFormatException(line);
		} catch (NumberFormatException  nfe)  {
			throw  new  StudentFormatException(line);
		}
		
		return v;
	}
}