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help with event handling

Popot Aartsen

Joined: Oct 11, 2002
Posts: 5
If you really have time to help a newbie
I am new to java programming, and my mind still with the old structured programming. I do understand about object, inheritance, polymorphic, method, interface, abstract data type. But, when it comes to EVENT handling, I lost Usually in structured programing, you can follow the flow.
So, in order to be more understand, could you please give me some VERY simple (easy to understand) example code to do :
// this is just a generic algorithm
main_program () {
write "1 = sub1";
write "2 = sub2";
write "0 = exit program";
key = get_a_key ();
if (key = "1") { sub_program1 (); }
if (key = "2") { sub_program2 ("HELLO"); }
until key = "0";
exit(); // exit program
sub_program1 () {
b = 0;
a = 0;
c = get_keypressed;
write a; // flood the screen with number
a = a + 1;
until c = <exit_key>;
write b;
b = b + 1;
until b = 3;
return; // go back to main program
sub_program2 (s) {
write s;
My objective here is to learn how to call a subprogram, and designing event handler in object oriented way.
Bal Mark

Joined: Sep 27, 2002
Posts: 19
Not going to translate your code .. but as for handling the events .. its done using listeners.
If you want to listen to key events .. get the object that you want to listen to (ie. a JTextField ) and add a KeyListener to it using the addKeyListener(KeyListener) on the JTextField you created
This is basically telling the JTextField where to go if you want to look at the keys pressed and do stuff on them ..
erm ok .. an example
(ps. a KeyAdapter is just a KeyListener with empty methods so you just override the methods you want to use )
JTextField f = new JTextField();
f.addKeyListener(new KeyAdapter(){
public void keyPressed(KeyEvent e){
if(e.getKeyCode() == KeyEvent.VK_ENTER){
System.out.println("Enter was just pressed");

now when you press enter in that JTextField it'll print a message "Enter was just pressed"
Dirk Schreckmann

Joined: Dec 10, 2001
Posts: 7023
If you're trying to better understand event-driven programming, you may appreciate the chapters in part 4 of Interactive Programming In Java by Lynn Andrea Stein.
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