[JAVA][Beginning Java 8 Games Development]

Chapter 3 ■ A Java 8 Primer: An Introduction to Java 8 Concepts and Principles
Fixing Data Values in Memory: Defining a Data Constant in Java
If you are already familiar with computer programming, you know that there is often a need to have data fields that
will always contain the same data value and that will not change during the duration of your application run cycle.
These are called constants, and they are defined, or declared, using special Java modifier keywords that are used
to fix things in memory so that they cannot be changed. There are also Java modifier keywords that will restrict (or
unrestrict) object instances, or access to certain classes inside or outside a Java class or package (which you will be
examining in detail in the next section).
To declare Java variables fixed, you must use a Java final modifier keyword. “Final” means the same thing as
when your parents say that something is final: it is fixed in place, an FOL (fact of life), and not going to change, ever.
Thus, the first step in creating a constant is to add this final keyword, placing it in front of the data type keyword in
your declaration.
A convention, when declaring a Java constant (and constants in other programming languages), is to use
uppercase characters, with underscored characters between each word, which signifies a constant in your code.
If you want to create screen width and screen height constants for your game, you do so like this:
final int SCREEN_HEIGHT_PIXELS = 480;
final int SCREEN_WIDTH_PIXELS = 640;
If you want all the objects created by your class’s constructor method to be able to see and use this constant, you
add the Java static modifier keyword, placing it in front of the final modifier keyword, like this:
static final int SCREEN_HEIGHT_PIXELS = 480;
static final int SCREEN_WIDTH_PIXELS = 640;
If you want only your class, and objects created by this class, to be able to see these constants, you declare the
constants by placing the Java private modifier keyword in front of the static modifier keyword, using this code:
private static final int SCREEN_HEIGHT_PIXELS = 480;
private static final int SCREEN_WIDTH_PIXELS = 640;
If you want any Java class, even those outside your package (i.e., anyone else’s Java classes), to be able to see
these constants, you declare the constants by placing the Java public modifier keyword in front of the static modifier
keyword, using the following Java code:
public static final int SCREEN_HEIGHT_PIXELS = 480;
public static final int SCREEN_WIDTH_PIXELS = 640;
As you can see, declaring a constant involves a significantly more detailed Java statement than declaring a simple
variable for your class! Next, you will take a deeper look at Java modifier keywords, as they allow you to control things
such as access to your classes, methods, and variables as well as locking them from being modified and similar highlevel
Java code control concepts that are fairly complicated.
Java Modifier Keywords: Access Control and More
Java modifier keywords are reserved Java keywords that modify the access, visibility, or permanence (how long
something exists in memory during the execution of an application) for code inside the primary types of Java
programming structures. The modifier keywords are the first ones declared outside the Java code structure, because
the Java logic for the structure, at least for classes and methods, is contained within the curly braces delimiter, which
comes after the class keyword and class name or after the method name and parameter list. Modifier keywords can be
used with Java classes, methods, data fields (variables and constants), and interfaces.
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