[JAVA][Beginning Java 8 Games Development]

Chapter 3 ■ A Java 8 Primer: An Introduction to Java 8 Concepts and Principles
}
}
btn.setText("Say 'Hello World'");
// The other programming statements continue underneath here
When the object declaration and instantiation are split up, they can be placed inside (or outside) methods as
needed for visibility. In the preceding code, other methods of your InvinciBagel class could call the .setText() method
call shown without the Java compiler’s throwing an error. The way the Button object is declared in Figure 3-2, only the
.start() method can see the object, and so only the .start() method can use this btn.setText() method call.
Creating a Constructor Method: Coding an Object’s Structure
A constructor method is more a method for creating objects in system memory, whereas other methods (or functions,
if using a different programming language) are usually used to perform calculation or processing of one type or
another. The constructor method’s use in creating Java objects in memory, rather than performing some other
programming function, is evidenced by the use of the Java new keyword, which creates a new object in memory. For
this reason, a constructor method will define the structure of an object as well as allow the calling entity to populate
the object structure with custom data values, using the constructor method’s parameter list.
You will create a couple of sample constructor methods in this section to learn the basics of how this is done as
well as what a constructor method usually contains. Let’s say you are creating an InvinciBagel object for your game,
so you declare a public InvinciBagel() constructor method, using the following Java code structure:
public InvinciBagel() {
int lifeIndex = 1000; // Defines units of lifespan
int hitsIndex = 0; // Defines units of damage ("hits" on the object)
String directionFacing = "E"; // Direction that the object is facing
Boolean currentlyMoving = false; // Flag showing if the object is in motion
}
This constructor method, when called using an InvinciBagel mortimer = new InvinciBagel(); Java method
call, creates an InvinciBagel object named mortimer, with 1,000 units of life and no hits, that is facing east and that is
not currently moving.
Next, let’s explore the concept of overloading the constructor method, which you learned about earlier
(see the section “Java Methods: Java Core Function Code Constructs”), and create another constructor method that
has parameters that allow you to define the lifeIndex and directionFacing variables of the InvinciBagel object while
you are creating it. This constructor method looks like this:
public InvinciBagel(int lifespan, String direction) {
int lifeIndex;
int hitsIndex;
String directionFacing = null;
Boolean currentlyMoving = false;
lifeIndex = lifespan;
directionFacing = direction;
}
54
www.it-ebooks.info