עיצוב תוכנה מונחה עצמים תירגול 1

1.Packages and Paths 2.Jar Files Outline

Package rules:  Each class belongs to a package  Package may have sub-packages  A package path is dot-separated  foo.goo.Boo Class Boo, sub-package goo, package foo  Sub-packages has no special properties or privileges Packages

Package declaration package foo.goo; class Boo {...} Package (cont'd) Importing classes from other packages import fi.fy.Fum; // Just class Fum import bar.baz.*; // All classes in bar.baz

When looking for a class, the JRE looks for a.class file in directories that match the package path: Sub-package = Sub-directory. The root directory is the classpath. Finding a Class Find the class foo.goo.Boo in the directories tree +-classpath | foo | goo |-X.class |-Y.class |-Boo.class

A classpath can contain several roots Finding a Class (cont'd) Finding foo.goo.Boo in classpath=A:B:C A +-A +-fi +-fy |-Fum.class |-... B +-B | foo | goo |-X.class |-Y.class C +-C | foo | goo |-W.class |-Z.class |-Boo.class

Jar files are the Java equivalent to libraries and executables. A jar file is a zip archive that contains: .class files  Other needed resources (images, config files)  A manifest file (optional)  Source files (optional) Jar Files

The manifest file is a text file with key: value properties. The JRE reads these properties when it loads the.jar file. Important properties in a jar manifest  Manifest-Version: For backward compatibility.  Main-Class: The class containing the main method to run.  Class-Path: Space-separated list of other class paths to use. See for details on jar and manifest specifications. The Manifest File

Manifest.mf Manifest-Version: 1.0 Main-Class: a.b.c.Foo Class-Path: mylib1.jar mylib2.jar Manifest example

Jar files as Java executables You can run a jar file by running: java -jar jar-file (Or double-click on it, in some systems) The Java Runtime will load all the content of the jar, including its classpath, and will run the main class that is written in the manifest. Using Jar files Jar files as Java shared libraries Including a jar file in a classpath will cause the JRE to look in the archive for classes and resources, as if it was another directory.

Creating a jar file using the command-line tool: jar cf files... Creating Jars