Java Reference
In-Depth Information
Java syntax: Procedure definition
public void procedure -name ( parameter-declarations ) {
sequence of statements
Purpose : To define a procedure named procedure -name , declare its
parameters, and give the sequence of statements to execute when the
procedure is called. Each parameter declaration has the form type vari-
able , and adjacent parameter declarations are separated by commas.
import javax.swing.*;
public class OurFrame extends JFrame {
place here the declaration of method setTitleToOrigin
Class OurFrame is called a subclass of JFrame , and JFrame is a superclass
of OurFrame . OurFrame acts just like a JFrame in most ways, but it is customized
to have additional behavior.
The first line of file makes available to the file all the class-
es in package javax.swing . The rest of the lines define class OurFrame .
Keyword public indicates that this class is accessible to all other classes. The
clause extends JFrame says that an instance of this class has all the components
—methods and variables— that a JFrame has.
We encourage you to type in this class (everything but the italicized words),
compile it, and try using it just as you did JFrame . Method setTitleToOrigin
has not yet been defined, so your new class will behave in every way like a
JFrame .
We now add the declaration of method setTitleToOrigin within the curly
braces { and } . Below is your first method declaration:
/** Set the title of this instance to contain the origin of the window */
public void setTitleToOrigin() {
place here statements to set the title
Style Note
13.1, 13.1.3
class names
Style Note
13.2, 13.2.4
for methods
Keyword public indicates that this method is accessible from anywhere.
Keyword void indicates that the method being defined is a procedure. Within the
curly braces we will place the statements that set the title to the origin. The curly
braces, together with any statements in between, constitute the body of the
We encourage you to type this method into class OurFrame (everything but
the italicized words). After compiling, you can now call ourWindow.setTitle-
ToOrigin(); (although nothing will happen yet).
We now figure out how to set the title. We want to place something like this
statement in the body of method setTitleToOrigin :
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