I have decided to come up with a series of Java tutorials teaching simple Java. This is my first chapter.

For this chapter, I will be showing how to write a simple program that:
1. Pops up a JOptionPane,
2. Shows a message on the pane.

Classes, Objects
Java, as some of you might already know, is a/an (almost) completely object-orientated programming language (OOP). Some of the experts out there may argue that Java is fully object-orientated, but I don't think that is absolute. Some programmers consider Ruby to be fully OOP and Java to be almost fully OOP because Java still uses primitive data types. (I don't know much on this, but if you do, please PM me. I love to learn.)

Object-orientated means that the program works with objects. An object is something that contains data and methods. A class defines the object, specifying what information the object should hold and what methods can be called. (methods are also known as functions)

An analogy:
"Humans" can be considered to be a class. Objects of this class should have a name, an age, a gender, and a bloodtype. The objects should be able to talk, sleep, eat, and see. "John" is an object. His name is John, age 18, male, bloodtype O. Like all humans, he talks, sleeps, eats, and sees.

Human -> Class
John -> Object
name, an age, a gender, and a bloodtype -> information
talk, sleep, eat, and see -> methods

The Code
To start coding, you need Java 2 Standard Edition Runtime Environment and Development Kit (J2RE and JDK, which can be downloaded from java.sun.com) and a compiler. I recommend Dr. Java, which can be downloaded from drjava.org.

In Java, everything is held within a class. Even the main method is enclosed within a class. So we start by typing this in:



Now, we need to DECLARE the objects we need (e.g. we need to declare a human "john"):



The above declares a window object and a point object, from the javax.swing package and the java.awt package.

Next, we need to CREATE the objects we need (e.g. creating John's body):



Then we give the characteristics:



Finally, we make it visible:



The final code looks like this:



Type the above into Dr Java, compile and hit F2 to run. There you go!. Do leave a message to ask for help if you need.

 

 

 

Reply

First of all, I see no JOptionPane. JFrames aren't the same thing. Second, why don't you import anything? It makes it less messy and you don't have to type the whole package tree every time you want to do something. You didn't setDefaultCloseOperation either, which can cause some problems.

Reply