Download Packages - Tonga Institute of Higher Education

Packages
Tonga Institute of Higher
Education
Pre-Built Objects and Methods
Method Name
System.out.println("We Miss Dave!");
Package


Java has many pre-built objects for us to use.
Doorknob analogy





Parameter
We want to add a doorknob to a door.
We could make our own.
But it’s easier to use a pre-built doorknob.
We still need to do work to add the doorknob to our door.
You can find a list of pre-built objects in the Java
Developer’s Kit documentation.
Demonstration
Java API Documentation
Organizing Classes

Java comes with over 2,700 different
classes for doing different things.

Sun needed a way to organize the classes
into groups, they decided to use
packages.

A package is a group of related classes.
Packages
Java contains 140 different packages.
 These packages are arranged
hierarchically (packages inside of
packages).

java
awt
event
geom
lang
image
ref
reflect
security
acl
spec
Package Names

The name of the package is actually a list
of names, separated by periods.
java.awt.image;
java
awt
event
geom
lang
image
ref
reflect
security
acl
spec
Using Packages


If you want to use a built-in Java class, first look it up in
the Java Application Interface. (API)
You can find the Java API documentation on the course
website page.

http://www.tihe.org/courses/it151
This is the API entry for the Graphics class.
The package for this class is java.awt.
Using Packages (cont.)

Once you know the package for a class,
import it into your program.
import java.awt.Graphics;

To import all classes in a package, use the
wild card (*).
import java.awt.*;
Case Study: Problem

Michael wants to use the Socket class in
his program for Networking.

Which package does he need to include in
his program?

What is the line of code he needs to write?
Case Study: Answer

Look up the Socket class in the Java API

Use the import command to include the
package:
import java.net.Socket;
or
import java.net.*;
Defining a Package

If you want to make your own package to be
used in other programs, define it.
package myprojects.helloworld;


Defining packages can lead to problems
compiling your program.
If you have multiple files in your project, make
sure they are all defined in the same package.