The objective of this tutorial is to introduce object-oriented programming and how to apply object-oriented thinking in program development.  our first Java application displays a window on the screen.  The size of the window is set to 300 pixels wide and 200 pixels high.  A pixel is a shorthand for picture element, and it is the standard unit of measurement for the screen resolution.  A common resolution for a 17-in monitor, for example, is 1024 pixels wide and 768 pixels high.  The title of the window is My First Java Program.

This is a very simple program, however, it still illustrates the fundamental structure of an object-oriented program. An object-oriented program uses objects; I bet you already knew that.

/* Example Program: Displaying a Window Zonehacks.com */ import javax.swing.*; class FirstApp { public static void main( String[] args ) { JFrame myWindow; myWindow = new JFrame(); myWindow.setSize(300,200); myWindow.setTitle("My First Java Program"); myWindow.setVisible(true); } }

This program declares one class called FirstApp, and the class includes one method called main.  From this main method, the FirstApp class creates and uses a JFrame object named myWindow by sending the three messages setSize, setTitle, and setVisible to the object.  The JFrame class is one of many classes that come with Java.  This instance of JFrame class is used to represent a single window on the computer screen. 

Something helpful to remember is:  To use an object in a program, first we must declare and create an object, and then we send messages to it.