The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
To make types easier to find and use, to avoid naming conflicts, and to control access, programmers bundle groups of related types into packages.
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: