Download mainWindow.setVisible( true )

Java Program Components
A Java program is composed of
comments,
import statements, and
class declarations.
DoDEA Summer 2002
Java
Monday - 1
Template for Simple Java Applications
center of the screen, and the size of the
window
is almost as big as the screen.
*/
import javabook.*;
class MyFirstApplication
{
Comment
Import
Statements
Class Name
public static void main(String[ ] args)
{
MainWindow
mainWindow;
Method Body
mainWindow = new MainWindow();
mainWindow.setVisible( true );
}
}
DoDEA Summer 2002
Java
Monday - 2
Program Component: Comment
/*
Program MyFirstApplication
This program displays a window on the screen. The window is
positioned at the center of the screen, and the size of the
window is almost as big as the screen.
*/
import javabook.*;
class MyFirstApplication
{
public static void main(String[ ] args)
{
MainWindow
Comment
mainWindow;
mainWindow = new MainWindow();
mainWindow.setVisible( true );
}
}
DoDEA Summer 2002
Java
Monday - 3
Three Types of Comments
/*
This is a comment with
Multiline Comment
three lines of
text.
*/
// This is a comment
// This is another comment
Single line Comments
// This is a third comment
/**
* This is a javadoc comment that allows for the
* automatic generation of web-page documentation
javadoc Comments
* if the correct format is followed.
*/
DoDEA Summer 2002
Java
Monday - 4
Program Component: Import Statement
/*
Program MyFirstApplication
This program displays a window on the screen. The window is
positioned at the center of the screen, and the size of the
window is almost as big as the screen.
*/
Import Statement
import javabook.*;
class MyFirstApplication
{
public static void main(String[ ] args)
{
MainWindow
mainWindow;
mainWindow = new MainWindow();
mainWindow.setVisible( true );
}
}
DoDEA Summer 2002
Java
Monday - 5
Import Statement Syntax and Semantics
Class Name
The name of the class we
want to import. Use asterisks
to import all classes.
Package Name
Name of the package that
contains the classes we
want to use.
Examples
DoDEA Summer 2002
<package name>
.
e.g.
.
javabook
import
import
<class name> ;
InputBox;
javabook.*;
java.awt.image.ColorModel;
Java
Monday - 6
Program Component: Class Declaration
/*
Program MyFirstApplication
This program displays a window on the screen. The window is
positioned at the center of the screen, and the size of the
window is almost as big as the screen.
Class Declaration
*/
import javabook.*;
class MyFirstApplication
{
public static void main(String[ ] args)
{
MainWindow
mainWindow;
mainWindow = new MainWindow();
mainWindow.setVisible( true );
}
}
DoDEA Summer 2002
Java
Monday - 7
Program Component: Method Declaration
/*
Program MyFirstApplication
This program displays a window on the screen. The window is
positioned at the center of the screen, and the size of the
window is almost as big as the screen.
*/
Method Declaration
import javabook.*;
class MyFirstApplication
{
public static void main(String[ ] args)
{
MainWindow
mainWindow;
mainWindow = new MainWindow();
mainWindow.setVisible( true );
}
}
DoDEA Summer 2002
Java
Monday - 8
Your First Java Application
A program to display a window on the screen using
the javabook package.
The size of the window is slightly smaller than the
screen, and the window is positioned at the center of
the screen.
A class in an application must have a “main” method
where execution begins.
DoDEA Summer 2002
Java
Monday - 9
Your First Java Application
A program to display a window on the screen using
the javabook package.
The size of the window is slightly smaller than the
screen, and the window is positioned at the center of
the screen.
The fundamental OOP concept illustrated by the
program:
An object-oriented program uses objects.
(e.g., mainWindow is the object)
DoDEA Summer 2002
Java
Monday - 10
Program MyFirstApplication
/*
Program MyFirstApplication
This program displays a window on the screen. The window is
positioned at the center of the screen, and the size of the
window is almost as big as the screen.
*/
import javabook.*;
class MyFirstApplication
{
public static void main(String[ ] args)
{
MainWindow
mainWindow;
Declare a name
mainWindow = new MainWindow();
Create an object
mainWindow.setVisible( true );
Make it visible
}
}
DoDEA Summer 2002
Java
Monday - 11
Flow of the MyFirstApplication Program
MainWindow
mainWindow;
mainWindow = new MainWindow(“Sample Java Application);
mainWindow.setVisible( true );
mainWindow
MainWindow
State-of-Memory Diagram
DoDEA Summer 2002
Java
Monday - 12
Steps in Executing Java Applications
Step 1 Edit
Type in the program using an editor and save the
program to a source file (className.java).
Step 2 Compile
Compile the source file to create the bytecode file
(className.class).
Step 3 Run
Execute the compiled source file called bytecode
file.
We’ll use and free IDE called jGrasp to perform steps 1-3.
DoDEA Summer 2002
Java
Monday - 13
The javabook Package
We used predefined classes from the javabook package. To
download the package or get its detailed documentation, please
visit Dr. Caffeine's web site at www.drcaffeine.com.
Advantages of using javabook:
Gives you a taste of how real-world programs are developed.
Minimizes the impact of programming language syntax and
semantics.
Allows you to write practical programs without learning too
many details.
Serves as good example of how to design classes.
DoDEA Summer 2002
Java
Monday - 14