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The types that are part of the Java platform
are members of various packages that bundle classes by function:
fundamental classes are in java.lang, classes for
reading and writing (input and output) are in java.io,
and so on. You can put your types in packages too.
Suppose you write a group of classes
that represent graphic 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.
//in the Draggable.java file
public interface Draggable {
. . .
}
//in the Graphic.java file
public 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 Point.java file
public class Point extends Graphic implements Draggable {
. . .
}
//in the Line.java file
public class Line extends Graphic implements Draggable {
. . .
}
You should bundle these classes and the interface in a package
for several reasons, including the following:
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