Java

Writing Applets

Applets are programs that run inside of a web page using the resources the web browser has to offer such as a Java Virtual Machine (JVM) and the default set of class libraries.

When you initially hit a web page with an incorporated Java applet, you usually see a gray box where the applet will show up and then slowly, the applet loads and appears in the space of the gray box.

Building an Application

Okay, so now let’s look at the rest of the Test class because the Test class is pretty special. The Test class is actually a very small Java Application that can be compiled and executed!

Here is the code again…

public class Test
  {
  public static void main(String[] args)
    {
    Announcer a = new Announcer();
    a.printAnnouncement();
    }
  }

You should already be comfortable with the definition of the class from the last section. You should also be familiar with the contents of the main() method since we just discussed it. But what is the main() method and why is there no constructor for Test?

Defining a Class

So right after the “public” keyword, we see the “class” keyword. The class keyword is used to specify that the following statement block defines a class. The class can be used to instantiate an object that is defined by the class. In our example case, we are defining a class called “Announcer”.

By the way, a class is usually defined in a “.java” file that is compiled into bytecode by a compiler into a “.class” file. Typically, your .java and .class filenames will be equivalent to the class name. Thus, the Announcer class would be stored in a file called Announcer.java and be compiled into a file named Announcer.class.

Operator Overloading

Another cool feature of Java is that methods in Java can easily be overloaded such that the same method name can be used for several different implementations of the same action. Remember our previous example of printNumber(), printLetter(), printImage()?

The only requirement for overloading is that each version of the method takes a different set of parameters as arguments (sometimes, we say that it has a “different signature”) such as in the following example:

Classes

OK, so now that we understand the most basic Java syntax it is time to learn how object-oriented design is implemented in Java.

The essential unit of article introduction in Java is the class. The class is often described as a blueprint for an object. It enables a software engineer to characterize the majority of the properties and techniques that inside characterize an article, the majority of the API strategies that remotely characterize an item, and the majority of the sentence structure vital for taking care of embodiment, legacy and polymorphism.