Student: ex07

Introducing packages

Part of a series of tutorial articles about a Student class.

Code examples referred to on this page can be found here: https://github.com/ucsb-cs156/student-tutorial/tree/ex07.

Overview

We move our code into a package in this example.

Introducing Packages

Real world Java code typically involves code from many authors, including third-party Java code; code written by others that you use in your project.

In order to keep all of the names of classes from colliding with one another, Java has the concept of packages. At the top of any class, you can put a line such as:

package edu.ucsb.cs156.student_tutorial;

This indicates that the code inside the .java file is part of the package edu.ucsb.cs156.student.

This needs to be the first line of code in the file, before any import statements, and typically before any comments as well.

The naming convention is often “reverse domain name”, i.e. if you are part of ucsb.edu, you flip this so that the names go from most general, to most specific, hence: edu.ucsb.cs156.student.

Along with the package, there is a requirement to put the code (both .java files and the produced .class files) into a directory hierarchy that mirrors the package names.

So to put our code into the package edu.ucsb.cs156.student, we need to create directories:

mkdir -p src/main/java/edu/ucsb/cs156/student
mv src/main/java/*.java src/main/java/edu/ucsb/cs156/student
mkdir -p src/test/java/edu/ucsb/cs156/student
mv src/test/java/*.java src/test/java/edu/ucsb/cs156/student

We then add the line package edu.ucsb.cs156.student_tutorial; to the top of each of our source files. The line doesn’t change depending on whether it’s part of the src/main/java or the src/test/java directory.