1. Tonga Institute of Higher Education
Packages
Tonga Institute of Higher Education

2. Pre-Built Objects and Methods
Method Name
System.out.println("We Miss Dave!");
Package
Parameter
Java has many pre-built objects for us to use.
Doorknob analogy
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.

3. Java API Documentation
Demonstration
Java API Documentation

4. 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.

5. Packages Java contains 140 different packages.
These packages are arranged hierarchically (packages inside of packages).
java
awt
event
geom
image
lang
ref
reflect
acl
security
spec

6. Package Names
The name of the package is actually a list of names, separated by periods.
java.awt.image;
java
awt
event
geom
image
lang
ref
reflect
acl
security
spec

7. 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.
This is the API entry for the Graphics class. The package for this class is java.awt.

8. Using Packages (cont.)
Once you know the package for a class, import it into your program.
To import all classes in a package, use the wild card (*).
import java.awt.Graphics;
import java.awt.*;

9. 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?

10. Case Study: Answer Look up the Socket class in the Java API
Use the import command to include the package: or
import java.net.Socket;
import java.net.*;

11. Defining a Package
If you want to make your own package to be used in other programs, define it.
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.
package myprojects.helloworld;