[JAVA][Beginning Java 8 Games Development]

Chapter 3 ■ A Java 8 Primer: An Introduction to Java 8 Concepts and Principles
Java’s final Modifier: Variables, Methods, and Classes That Cannot Be Modified
You have already explored the final modifier keyword as it is used to declare a constant, along with a static keyword.
A final data field variable can only be initialized (set) one time. A final reference variable, which is a special type of
Java variable that contains a reference to an object in memory, cannot be changed (reassigned) to refer to a different
object; the data that are held inside the (final) referenced object can be changed, however, as only the reference to the
object itself is the final reference variable, which is essentially locked in, using a Java final keyword.
A Java method can also be locked using the final modifier keyword. When a Java method is made final, if the Java
class that contains that method is subclassed, that final method cannot be overridden, or modified, within the body
of the subclass. This basically locks what is inside the method code structure. For example, if you want the .start()
method for your InvinciBagel class (were it ever to be subclassed) always to do the same things that it does for your
InvinciBagel superclass (prepare a JavaFX staging environment), you use the following code:
public class InvinciBagel extends Application {
Button btn;
}
@Override
public final void start(Stage primaryStage) {
btn = new Button();
// The other method programming statements continue here
}
This prevents any subclasses (public class InvinciBagelReturns extends InvinciBagel) from changing anything
regarding how the InvinciBagel game engine (JavaFX) is set up initially, which is what the .start() method does for
your game application (see Chapter 4). A class that is declared using a final modifier keyword cannot be extended, or
subclassed, locking that class for future use.
Java’s Static Modifier: Variables or Methods That Exist in a Class (Not in Objects)
As you have already seen, the static keyword can be used in conjunction with the final keyword to create a constant.
The static keyword is used to create Java constructs (methods or variables) that exist independently, or outside, any
object instances that are created using the class that static variables or static methods are defined in. A static variable
in a class will force all instances of the class to share the data in that variable, almost as if it is a global variable as far as
objects created from that class are concerned. Similarly, a static method will also exist outside instanced objects for
that class and will be shared by all those objects. A static method will not reference variables outside itself, such as an
instanced object’s variables.
Generally, a static method will have its own internal (local or static) variables and constants and will also take in
variables, using the method parameter list, and then provide processing and computation, based on those parameters
and its own internal (static local) constants if needed. Because static is a concept that applies to instances of a class,
and is thus at a lower level than any class itself, a class would not be declared using a static modifier keyword.
Java’s Abstract Modifier: Classes and Methods to Be Extended and Implemented
The Java abstract modifier keyword has more to do with protecting your actual code than with code that has been
placed in memory (object instances and variables, and so on) at runtime. The abstract keyword allows you to specify
how the code will be used as a superclass, that is, how it is implemented in a subclass once it is extended. For this
reason, it applies only to classes and methods and not to data fields (variables and constants).
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