JAVA help

I'm having some trouble in my java class at school. We are making a calculator program. I have the display and buttons and everything good. The only thing i need help on is getting the numbers up to the text field after i press the button. We arn't worrying about multiplication, addition or anything yet, so i dont think this will be too hard. The numbers just have to appear up in the text field. This is what i have so far.

import java.applet.*; import java.awt.*; public class Calculator extends Applet { private TextField screen; public void init () { this.setLayout(new GridLayout(3, 1, 3, 3)); Panel A1 = new Panel(); this.add(A1); Panel A2 = new Panel(); this.add(A2); Panel A3 = new Panel(); this.add(A3); A1.setLayout(new GridLayout(2, 1)); screen = new TextField(12); A1.add(screen); Panel B1 = new Panel(); B1.setLayout(new GridLayout(1, 4, 3, 3)); B1.add(new Button("C")); B1.add(new Button("=")); B1.add(new Button("/")); B1.add(new Button("*")); A1.add(B1); A2.setLayout(new GridLayout(2, 4, 3, 3)); A2.add(new Button("7")); A2.add(new Button("8")); A2.add(new Button("9")); A2.add(new Button("C")); A2.add(new Button("4")); A2.add(new Button("5")); A2.add(new Button("6")); A2.add(new Button("+")); A3.setLayout(new GridLayout(1, 2, 3, 3)); // 1, 2 and 0 Panel B2 = new Panel(); B2.setLayout(new GridLayout(2, 1, 3, 3)); // 1 and 2 Panel C1 = new Panel(); C1.setLayout(new GridLayout(1, 2, 3, 3)); C1.add(new Button("1")); C1.add(new Button("2")); B2.add(C1); B2.add(new Button("0")); // 3, . and = Panel B3 = new Panel(); B3.setLayout(new GridLayout(1, 2, 3, 3)); // 3 and . Panel C2 = new Panel(); C2.setLayout(new GridLayout(2, 1, 3, 3)); C2.add(new Button("3")); C2.add(new Button(".")); B3.add(C2); B3.add(new Button("=")); A3.add(B2); A3.add(B3); } public Insets getInsets() { return new Insets(5, 5, 5, 5); } }