Packages

Tonga Institute of Higher Education

Pre-Built Objects and Methods

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.

System.out.println("We Miss Dave!");System.out.println("We Miss Dave!");

Method Name

ParameterPackage

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

image

lang

ref reflect

acl

security

spec

Package Names

The name of the package is actually a list of names, separated by periods.

java

awt

event

geom

image

lang

ref reflect

acl

security

spec

java.awt.image;

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.

To import all classes in a package, use the wild card (*).

import java.awt.Graphics;

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:

orimport java.net.Socket;

import java.net.*;

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;