Conditionals and Loops - Java Software Solutions: Foundations of Program Design - page 248

SELF-REVIEW QUESTIONS
SR 5.26 What are the advantages of using an ArrayList object?
SR 5.27 What type of elements does an ArrayList hold?
SR 5.28 Write a declaration for a variable named dice that is an ArrayList of
Die objects.
SR 5.29 What output is produced by the following code fragment?
ArrayList<String> names = new ArrayList<String>();
names.add ("Andy");
names.add ("Betty");
names.add (1, "Chet");
names.add (1, "Don");
names.remove (2);
System.out.println (names);
5.7 Determining Event Sources
In Chapter 4 we began our exploration of creating programs with a truly interac-
tive graphical user interface (GUI). You'll recall that interactive GUIs require that
we create listener objects and set up the relationship between listeners and the
components that generate the events of interest.
Let's look at an example in which one listener object is used to listen to two
different components. The program represented by the LeftRight class, shown
in Listing 5.12 displays a label and two buttons. When the left button is pressed,
the label displays the word Left, and when the right button is pressed, the label
displays the word Right.
The LeftRightPanel class, shown in Listing 5.13, creates one instance of the
ButtonListener object, then adds that listener to both buttons. Therefore, when
either button is pressed, the actionPerformed method of the ButtonListener
class is invoked.
On each invocation, the actionPerformed method uses an if-else statement
to determine which button generated the event. The getSource method is called
on the ActionEvent object that the button passes into the actionPerformed
method. The getSource method returns a reference to the component that gener-
ated the event. The condition of the if statement compares the event source to
the reference to the left button. If they don't match, then the event must have been
generated by the right button.