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JAVA PROGRAMMING

What packages are and their uses?

To make classes easier to find and use, to avoid naming conflicts, and to control access, programmers bundle groups of related classes into packages. 

A package is a collection of related classes and interfaces that provides access protection and namespace management. 

The classes and interfaces that are part of the JDK are members of various packages that bundle classes by function: applet classes are in java.applet, I/O classes are in java.io, and the GUI widget classes are in java.awt. You can put your classes and interfaces in packages, too. 

Let's look at a set of classes and examine why you might want to put them in a package. Suppose you write a group of classes that represent a collection of graphics objects such as circles, rectangles, lines, and points. You also write an interface Draggable that classes implement if they can be dragged with the mouse by the user. 

in the Graphics.java file
abstract class Graphic {
. . .
}

in the Circle.java file
public class Circle extends Graphic implements Draggable {
. . .
}

in the Rectangle.java file
public class Rectangle extends Graphic implements Draggable {
. . .
}

in the Draggable.java file
public interface Draggable {
. . .
}

You should bundle these classes and the interface together in a package, for several reasons: 
You and other programmers can easily determine that these classes and interfaces are related. 
You and other programmers know where to find classes and interfaces that provide graphics-related functions. 
The names of your classes won't conflict with class names in other packages because the package creates a new namespace. 
You can allow classes within the package to have unrestricted access to each other, yet still restrict access for classes outside the package.