Articles : JavaBoutique's Introduction to Java :
Java Classes :

Instantiating and Using an Object

So where are these other objects and how is an Announcer object actually "instantiated"?

To instantiate an object, Java uses the keyword "new". Consider the following class called Test that instantiates an Announcer and then uses its public API to print the announcement.

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

We won't yet focus on the syntax of the Test class. Instead we will just focus on how the Test class utilizes the Announcer class. Notice that the Test class use the new keyword to instantiate an Announcer object and then calls the printAnnouncement() method on the Announcer object using the "dot notation".

The dot notation is used to access properties or methods in an object. In this case, we have an Announcer object named "a" and we will access the printAnnouncement() method in a.

It is crucial that you specify the object that you want to utilize because it is very possible that there may be more than one Announcer object alive at any given time. Thus, you need to specify which Announcer object you want to access the printAnnouncement method on. Consider the following case in which we apply all of what we just learned about classes. In this example we will create three Announcer objects, two using the default constructor and one using the alternate constructor. We will then use the setAnnouncement API method to change the announcement of the second object and then have each Announcer object print out its announcement using the dot notation

public class Test
  {
  public static void main(String[] args)
    {
    Announcer a = new Announcer();
    Announcer b = new Announcer();
    Announcer c = new Announcer("Hello Sol");

    b.setAnnouncement("Hello World");

    a.printAnnouncement(); // prints Hello
			   //        Cyberspace
    b.printAnnouncement(); // prints Hello World
    c.printAnnouncement(); // prints Hello Sol
    }
  }

Selena Sol contributes to the JavaBoutique's Introduction to Java. Selena curently works for Barclays Capital in London, one of the leading global investment banks in Europe and has worked as a software developer for the National Center for Human Genome research, Microline Software, Neuron Data, and Electric Eye in Singapore. Selena is perhaps best-known for creating the Public Domain Web Script Archive (Extropia) and writing several books on Web Programming (Perl, CGI, Java).
Email: selena@extropia.com