Like a group of radio buttons, a drop-down list is a way to
force the user to select only one element from a group of possibilities.
However, itís a much more compact way to accomplish this, and itís easier to
change the elements of the list without surprising the user. (You can change
radio buttons dynamically, but that tends to be visibly jarring).
Javaís Choice box is not like the combo box in Windows, which lets you select
from a list or type in your own
selection. With a Choice box you
choose one and only one element from the list. In the following example, the Choice box starts with a certain number
of entries and then new entries are added to the box when a button is pressed.
This allows you to see some interesting behaviors in Choice boxes:
// Using drop-down lists
public class Choice1 extends Applet ;
TextField t = new TextField(30);
c = new Choice();
Button b = new Button('Add items');
int count = 0;
public void init()
public boolean action (Event evt, Object arg)
return super.action(evt, arg);
displays the ďselected index,Ē which is the sequence number of the currently
selected element, as well as the String
representation of the second argument of action( ),
which is in this case the string that was selected.
When you run this applet, pay attention to the determination
of the size of the Choice box: in
Windows, the size is fixed from the first time you drop down the list. This
means that if you drop down the list, then add more elements to the list, the
elements will be there but the drop-down list wonít get any longer (you can scroll through the elements).
However, if you add all the elements before the first time the list is dropped
down, then it will be sized correctly. Of course, the user will expect to see
the whole list when itís dropped down, so this behavior puts some significant
limitations on adding elements to Choice