Object-Oriented Introduction to Java - Multimedia Introduction to Programming Using Java - page 34

Java syntax: instance-function call
variable . name ( arguments )

Java syntax: instance-procedure call
variable . name ( arguments );

Example : w.getTitle() Example : w.setTitle("Peace");

Purpose : To call the function name that occurs
in the folder whose name is in variable vari-
able . A function call is an expression and does
not end in a semicolon.

Purpose : To call the procedure name that occurs in the
folder whose name is in variable variable . A procedure
call ends in a semicolon.

a reference to a component of the folder follows; the phrase “ show ” is a reference
to procedure show within that folder; and the parentheses indicate the (empty) list
of arguments. In general, in order to access a component (variable or method) of
a folder, use the form

< variable that contains the name of the folder > . < component-name >
We summarize how you can create and show on your monitor a window that
is associated with a JFrame. Just type the following three lines into the
Interactions pane of DrJava, and the window will appear in the upper left corner:

import javax.swing.*;
JFrame window;
window= new JFrame("first Title");
window.show();
The first line says that the classes in package javax.swing may be used.
The second line declares variable window . The fourth line creates a manila fold-
er of class JFrame and stores its name in window . The fourth line shows the win-
dow on the monitor.

Getter and setter methods
A folder of class JFrame contains lots of information about the window with
which it is associated. One can generally get this information using calls on cer-
tain functions that appear in each folder of the class. In Java parlance, these are
called getter methods because they get a value from the folder. For example,
below, we show a few function calls and the results of their evaluation:

function call value

title of the window

window.getTitle()

height of the window, in “pixels”

window.getHeight()

width of the window, in “pixels”

window.getWidth()

Thus, a getter method is a function that retrieves a value from an object.
A setter method is a procedure that sets (or changes) a value in an object. For
example, you can change the title of the window to “another title” by executing
the procedure call: