Simple applet - addition of two integers

Hi folks, as a relative "newbie" to this, I seem to have become slighty stuck on an applet! I need to write a simple applet which provides two TextField objects in which the user can enter positive numbers, one in each; the numbers should be summed and the result displayed in a Label object. The result should not be displayed until both numbers have been entered. The second number should be no longer than 3 digits.
Here is what I have so far:

/*an applet which demonstrates the use of text fields*/
import java.awt.*;

public class SimpleTextField extends java.applet.Applet
{
int num1, num2, num3;
Label l;
TextField tf1, tf2;

public void init()
{
add(new Label("Enter first number"));
tf1 = new TextField(3);
add(tf1);
l = new Label("Enter second number");
add(l);
tf2 = new TextField(3);
add(tf2);
}

public boolean action(Event evt, Object arg)
{
if (evt.target instanceof TextField)
{
if(evt.target == tf1)
{
num1 = tf1.getText();
}
else
{
if (tf2.getText().length() > 3)
{
l.setText("Number too long");
}
else
{
num2 = tf2.getText();
l.setText("valid number");
}
}
repaint();
}
return true;
}

public void paint(Graphics g)
{
g.drawString("The result of your two numbers is: " + num3, 10, 115);
}
}


I'm unsure where I need to put the code that adds the two numbers together.
Any help would be greatly appreciated.
Thanks!

You seem to be talking java

the text box values are strings so you will need to ensure the input is numbers only with no full stops then the string can be converted to an integer

Integer.valueOf(MyString);

the integers can then be added

much easier with javascript