[JAVA][Beginning Java 8 Games Development]

Chapter 10 ■ Directing the Cast of Actors: Creating a Casting Director Engine and Creating the Bagel Actor Class
The HashSet class implements the Set interface in the form of a hash table, which is actually an instance of
a HashMap. The HashSet makes no guarantees as to the iteration order of the Set of objects; in particular, it does
not guarantee that the order will remain constant over time. This class permits the use of one null element.
It is important to note that the Set implementation is not synchronized. If multiple threads access your
HashSet object concurrently, and at least one of these threads modifies your Set, then it should be synchronized
externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the Set
such as the HashSet. We are using the HashSet in a very basic fashion: to hold objects that are removed from the
game play for one reason or another, such as treasure being found; enemies being eliminated; or similar game design
scenarios.
One of the advantages of the HashSet class (and object) offers is a constant time performance for your basic
dataset operations such as the .add(), .remove(), .contains(), and .size() methods. Iteration over a HashSet object will
require a time period proportional to the sum of the Set object instance size, which is determined by the number
of elements currently in the Set combined with the “capacity” of the backing HashMap object instance.
Creating Your Casting Engine: CastingDirector.java
Now that you have some background on Java interfaces, the Java Collection Framework, and its List and
Set interfaces implemented by the ArrayList and HashSet classes, we can move on to create our basic
CastingDirector class. The class will keep a List object of what Actor objects are currently “in play” in the current
scene and another List object of what Actor objects should be checked for collisions. There will also be a Set object to
hold Actor objects that need to be removed. Right-click on the invincibagel package folder in the NetBeans Projects
pane, and select the New ➤ Java Class menu sequence to bring up the New Java Class dialog, which is shown in
Figure 10-2. Name the new class CastingDirector and leave the other fields in the dialog, which are automatically set
by NetBeans.
Figure 10-2. Create a New Java Class in the invincibagel package; name it CastingDirector for the InvinciBagel Project
We will start by creating the List ArrayList objects first, one to hold the current cast for
your scene and then a second List to hold objects to be checked for collision detection. After that we will
create the Set HashSet object, which will provide an unordered Set object, which will collect
those Actor objects that need to be removed from the scene. Let’s get started creating the body of our public
CastingDirector class.
www.it-ebooks.info
213