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Optimize with a SATA RAID Storage Solution
Range of capacities as low as $1250 per TB. Ideal if you currently rely on servers/disks/JBODs
Why reinvent the wheel? That cliche applies to software development where some developers frequently rewrite the same code for different programs. Two disadvantages with that approach are:
As an alternative to rewriting the same code, many software development environments provide a library tool that organizes frequently used code. Once developers finish debugging some reusable code, they use the tool to store that code in a library—one or more files that contain frequently used code for use in various programs. During program-building, the compiler or library tool accesses the library to connect the program's library-referenced code to the program.
Libraries are fundamental to Java. They allow, in part, the JVM's classloader to locate classfiles. (I will explore classloaders in a future article.) For that reason, Java's libraries are commonly known as class libraries. However, Java refers to class libraries as packages.
This article explores packages; I show you how to create packages of classes and interfaces, how to import (that is, bring into a program) packaged classes and interfaces, how to move packages on the hard drive, and how to use jar files to encapsulate packages.
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| This article's single package experiment is Microsoft Windows-specific. You should be able to easily extrapolate this experiment to non-Windows platforms. |
A package is a collection of classes and interfaces. Each package has its own name and organizes its top-level (that is, nonnested) classes and interfaces into a separate namespace, or name collection. Although same-named classes and interfaces cannot appear in the same package, they can appear in different packages because a separate namespace assigns to each package.
From an implementation perspective, equating a package with a directory proves helpful, as does equating a package's classes and interfaces with a directory's classfiles. Keep in mind other approaches—such as the use of databases—to implementing packages, so do not get into the habit of always equating packages with directories. But because many JVMs use directories to implement packages, this article equates packages with directories. The Java 2 SDK organizes its vast collection of classes and interfaces into a tree-like hierarchy of packages within packages, which is equivalent to directories within directories. That hierarchy allows Sun Microsystems to easily distribute (and you to easily work with) those classes and interfaces. Examples of Java's packages include:
java.lang: A collection of language-related classes, such as Object and String, organized in the java package's lang subpackage
java.lang.ref: A collection of reference-related language classes, such as SoftReference and ReferenceQueue, organized in the ref sub-subpackage of the java package's lang subpackage
javax.swing: A collection of Swing-related component classes, such as JButton, and interfaces, such as ButtonModel, organized in the javax package's swing subpackage
Period characters separate package names. For example, in javax.swing, a period character separates package name javax from subpackage name swing. A period character is the platform-independent equivalent of forward slash characters (/), backslash characters (\), or other characters to separate directory names in a directory-based package implementation, database branches in a hierarchical
database-based package implementation, and so on.