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<META name=vsisbn content="1571690433"><META name=vstitle content="Black Art of Java Game Programming"><META name=vsauthor content="Joel Fan"><META name=vsimprint content="Sams"><META name=vspublisher content="Macmillan Computer Publishing"><META name=vspubdate content="11/01/96"><META name=vscategory content="Web and Software Development: Programming, Scripting, and Markup Languages: Java"><TITLE>Black Art of Java Game Programming:Advanced Techniques</TITLE>
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<font face="arial, helvetica" size="-1" color="#336633"><b>Black Art of Java Game Programming</b></font>
<br>
<font face="arial, helvetica" size="-1"><i>by Joel Fan</i>
<br>
Sams, Macmillan Computer Publishing
<br>
<b>ISBN:</b> 1571690433<b> Pub Date:</b> 11/01/96</font>
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<H2><A NAME="Heading1"></A><FONT COLOR="#000077">Chapter 10<BR>Advanced Techniques
</FONT></H2>
<P><I>Joel Fan</I></P>
<P><FONT SIZE="+1"><B>Goals:</B></FONT></P>
<P>Learn advanced techniques you can use in games, including the use of packages, threads, image processing, and data structures in java.util
</P>
<P>In this chapter, you’ll learn a variety of techniques that will be useful in creating games and other applications. For example, you’ll see:</P>
<DL>
<DD><B>•</B> How to create packages that organize related collections of classes.
<DD><B>•</B> How to organize games and other applications with threads.
<DD><B>•</B> How to use java.awt.image for simple image processing. In particular, you’ll see how to reduce the download time of a series of bitmaps.
<DD><B>•</B> Data structures in java.util that make writing games easier.
<DD><B>•</B> Tips for creating applets that perform across a wide variety of platforms.
</DL>
<P>Feel free to skim this chapter and adapt whatever you need for your own projects. Let’s get started!
</P>
<H3><A NAME="Heading2"></A><FONT COLOR="#000077">Using Packages</FONT></H3>
<P>A <I>package</I> is a group of classes, interfaces, and/or subpackages that share a related purpose. Examples of packages are java.awt.image or java.lang. The <I>fully qualified name</I> of a class</P>
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<packagename>.<classname>
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<P>denotes the given class within the package. For example, the fully qualified name of the Graphics class, contained in package java.awt, is java.awt.Graphics.
</P>
<P>All classes in Java belong to some package. Within a class definition, you can refer to another class in the same package by using the class name alone. However, a class must use the fully qualified name when referring to a class outside of its own package.</P>
<H4 ALIGN="LEFT"><A NAME="Heading3"></A><FONT COLOR="#000077">Importing Packages and Classes</FONT></H4>
<P>It’s inconvenient to type the fully qualified name every time you want to refer to a class in another package. By <I>importing</I> a package or a class into your program, you can use class names alone.</P>
<P>Java supports three versions of the <I>import</I> statement:</P>
<DL>
<DD><B>•</B> <I>Import a single class</I>. Use the fully qualified name of the class in the <I>import</I> statement. Then, the class name alone will refer to the imported class. For example:
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// can refer to 'Graphics' in following code
import java.awt.Graphics;
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<DD><B>•</B> <I>Import all the classes in a package</I>. Use the package name, qualified by <TT>*</TT>, in the <I>import</I> statement. Then, all classes in the packages can be referred to by using only the class names.
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// can refer to all classes in java.awt using
// class name alone, i. e. 'Component', 'Graphics', ...
import java.awt.*;
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<DD><B>•</B> <I>Import the package</I>. Use the package name in the <I>import</I> statement:
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import java.awt;
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<BR>Then to reference a class, use the last component of the package name, followed by the class name, i.e., “awt.Graphics”.
</DL>
<H4 ALIGN="LEFT"><A NAME="Heading4"></A><FONT COLOR="#000077">Creating Packages</FONT></H4>
<P>You can create your own packages of classes and interfaces. This is useful for three reasons:
</P>
<DL>
<DD><B>•</B> <I>To organize related classes and interfaces</I>. A package gives related classes and interfaces conceptual unity. It’s a good idea to group libraries of class files into packages that you can import when necessary. An example of a set of related classes is the Sprite class we developed in Chapters 3, 4, and 5. To create a package called “sprite”, place the following statement
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package sprite;
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<BR>at the beginning of each file that contains code to a Sprite class. (The package declaration <I>must</I> be the first statement in the file.) If you don’t include a package statement at the start of a file, the classes in the file will be members of the default package.
<DD><B>•</B> <I>To avoid name conflicts</I>. By creating packages, you avoid the possibility of naming conflicts while developing applications. Let’s say you’re writing a program with your friend Ira. By putting all of Ira’s classes into a package called “ira”, and your classes into your own package, there won’t be any problems if you both pick the same names for classes. For example, if each package has a class Shark, the two versions can be distinguished using the fully qualified name:
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ira.Shark shark1; // Shark class in package ira
jon.Shark shark2; // Shark class in package jon
</PRE>
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<DD><B>•</B> <I>For visibility</I>. The classes in a package have direct access to all variables for which access isn’t specified (for example, <I>public</I>, <I>private</I>, <I>protected</I>), and to all classes within the package. You can use this default level of access to make the classes in a package more efficient, by eliminating unnecessary accessor methods while keeping these variables visible only within a package. Only the <I>public</I> classes and interfaces of a package are accessible outside of the package. Thus, you can create helper classes that are non-<I>public</I>, and invisible outside package boundaries.
</DL>
<H4 ALIGN="LEFT"><A NAME="Heading5"></A><FONT COLOR="#000077">Nested Packages and Directory Structure</FONT></H4>
<P>A package can be nested within another package. The declaration
</P>
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package game.sprite;
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<P>denotes a package “sprite” in a package called “game”. In a similar way, the packages of the Java API, such as java.lang and java.awt, are subpackages of the enclosing “java” package. Thus, packages are organized in hierarchical fashion.
</P>
<P>For many installations, the package hierarchy corresponds to the directory structure of the packages. Thus, class files of the package “game” belong in some directory called game/, while class files of package game.sprite are found in the directory game/sprite/. If you don’t state the package that a source file belongs to, it is considered part of the <I>default package</I>, which corresponds to the directory that the file is in.</P>
<P>When you’re developing a game, it’s easiest to keep your files as part of the default package. But once you’ve built up a library of classes you’ll use in future games, you can arrange these class files in packages and import them when necessary.</P>
<P>Now, let’s move on to threads.</P>
<H3><A NAME="Heading6"></A><FONT COLOR="#000077">Using Threads</FONT></H3>
<P>Threads are one of Java’s most powerful features. In Chapter 8, Implementing a High Score Server on a Network, you were introduced to threads and how they can be used to create networked games and applications. In this chapter, you will see further advantages and pitfalls of working with a “threaded approach” in your applets. First, let’s review the definition of a thread.
</P><P><BR></P>
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