Java Reference
In-Depth Information
When you execute the currently selected class, NetBeans compiles the code to a set
of binary files, and then transfers control to the
main()
method. That method, in turn,
does the following:
1.
Executes
HelloMessage hm
to create a variable named
hm
that is
capable of holding an instance of the class
HelloMessage
. The
variable
hm
is empty at this point.
2.
Invokes
new HelloMessage()
to create an object of the class by
that name. The no-arg constructor will be executed, and
"Default
Message"
is now the greeting text. The new object is now stored in
the variable
hm
.
3.
Makes a call to
System.out.println()
to show that the ob-
ject's no-arg constructor has indeed executed as expected. The greet-
ing
"DEFAULT MESSAGE"
is displayed in the “Output” pane.
4.
Sets the message to be the traditional text
"Hello, World"
.
5.
Makes another call to
System.out.println()
to output the
new message that has just been set. Now you see the greeting
"hello, world"
added to the “Output” pane.
The pattern in the solution is common in Java programming. The
main()
method
is where execution begins. Variables are defined, and objects are created using the
new
operator. Object variables are often set and retrieved using setter and getter methods.
Tip
Command-line apps are passé. System administrators and programmers some-
times write them as utilities, or to batch-process large amounts of data. But in the main,
today's applications are GUI applications. JavaFX is the way forward in writing those
applications, and you can learn about it in
Chapters 14
through
17
. Recipe 14-1 provides
what is essentially a “Hello, World” application in GUI form.
1-3. Compiling and Executing from the
Command-line Interpreter
Problem
