Solution

HTML Interface to Applet

<APPLET CODEBASE="/applets/magelang/AWT-Training/classes/" CODE="PhoneTextFieldTest.class" WIDTH=300 HEIGHT=20 ALIGN=CENTER></APPLET>

Java Code

import java.awt.*;
import java.util.*;

public class PhoneTextFieldTest extends java.applet.Applet {

    public void init() {
        setLayout(new GridLayout(1,1));
        PhoneTextField test = new PhoneTextField();
        add(test);
    }
}

/**
 * Component containing both a Label and a TextField.
 * Used for entering and validating a phone number.
 */
class PhoneTextField extends LabeledTextField {

    public PhoneTextField() {
        super("Phone Number");
    }

    public void verify() {
        StringBuffer    buffer = new StringBuffer();
        StringTokenizer st     = new StringTokenizer(text.getText(), "()- ");
        // remove parentheses, spaces and dashes
        while (st.hasMoreTokens()) {
            buffer.append(st.nextToken());
        }
        // make sure there are numbers
        try { Integer.parseInt(buffer.toString()); }
        catch (NumberFormatException e) {
            System.err.println("Only digits are allowed:  " +
                                "Please enter again.");
            text.setText("");
        }
        // right length?
        if (buffer.length() != 7 && buffer.length() != 10) {
            System.err.println("Not the right number of digits:  " +
                               "Please enter again.");
            text.setText("");
        }
    }
}