Goal: The goal of this assignment is to gain practical experience with data abstraction, unit testing and using the Java class libraries (the Java 8 SE API). 

Problem Overview: In this assignment, and the following two assignments in this course, you will develop the component classes of a program for simulating the behaviour of a train management system.  A train management system controls the behaviour of trains on a railway track. A railway track is composed of sections of track that are connected at junctions in the track. Each junction in the track has

between one and three connections to sections of track. Each of these connections is referred to as a branch of the junction, and each of those branches has a type: they are either a FACING, NORMAL or REVERSE branch. Each junction can only have one branch of each type. Locations on the track can be defined relative to their offset from a junction along one of its branches. 

Task Overview: In this assignment, you will be writing data types for a Section, a Location, and a Track.(All students will be expected to write their own tests to help them to debug their implementations,

but only CSSE7023 students will be required to submit their tests for the SectionTest class.)  Task Details:  Skeletons for the classes Section, Location and Track classes are provided in the zip file in the railway package. These skeletons include javadoc specifications of the constructors and methods that you need to complete. You must complete these class skeletons according to their specifications in the files. You

will need also to declare variables, add import clauses, and add comments and javadocs as required.  If you are a CSSE7023 student, you will also need to complete systematic and understandable JUnit4

test suite for the Section class in the skeleton of the SectionTest class from the railway.test package. You may write your unit tests assuming that the classes that Section depends on (e.g. the Junction class and any of the Java SE API libraries) are implemented and functioning correctly. That is, you don''t need to

create test stubs for these classes.  Copy or rename the skeleton files before you start. (Don''t forget that the package and class names inside the files must correspond to the file and the directory names ... otherwise you''ll have difficulty compiling

and running it.) 

You must implement these classes as if other programmers were, at the same time, implementing the code that instantiates them and calls their methods. Hence:  • Don''t change the class names, specifications, or alter the method names, parameter types, return types, exceptions thrown or the packages to which the files belong. 

• Don''t add any new methods or variables to the classes unless they are private (that would be changing their specification by adding new features accessible from outside the class).  • You are encouraged to use Java 8 SE API classes, but no third party libraries should be used. (It is not

necessary, and makes marking hard.)  • Don''t write any code that is operating-system specific (e.g. by hard-coding in newline characters etc.),

since we will batch test your code on a Unix machine.  • Your source files should be written using ASCII characters only.  Implement the classes as if other programmers are going to be using and maintaining them. Hence: 

• Your code should follow accepted Java naming conventions, be consistently indented, readable, and

use embedded whitespace consistently.  • Your code should use private methods and private instance variables and other means to hide implementation details and protect implementation invariants.  • Your methods, fields and local variables (except for-loop variables) should have appropriate Javadoc comments or normal comments.  • Comments should be used to document your code''s invariants, and to describe any particularly tricky sections. (You must provide an implementation invariant for each of the Section, Location and Track classes). However, you should also strive to make your code understandable without reference to

comments; e.g. by choosing sensible method and variable names, and by coding in a straightforward way. 

• Any exceptions that are created and thrown should have appropriate messages to help the user understand why the exception was thrown. 

• The checkInvariant() method of each class (other than the test suite) should check that the implementation invariant you have specified in your comments is satisfied. 

• Your code should not be overly complex and hard to understand.  The Zip file for the assignment also includes some other code that you will need to compile your classes as well as some junit4 test classes to help you get started with testing your code. 

Do not modify any of the files in package railway other than Section, Location and Track, since we will test your code using our original versions of these other files. Do not add any new files that your code for these classes depends upon, since you won''t submit them and we won''t be testing your code using

them.  The junit4 test classes as provided in the package railway.test are not intended to be an exhaustive test

for your code. Part of your task will be to expand on these tests to ensure that your code behaves as required by the javadoc comments. (Only if you are a CSSE7023 student will you be required to submit

your test file SectionTest.java.) We will test your code using our own extensive suite of junit test cases. (Once again, this is intended to mirror what happens in real life. You write your code according to the "spec", and test it, and then hand it over to other people ... who test and / or use it in ways that you may not have thought of.)  If you think there are things that are unclear about the problem, ask on the piazza forum, ask a tutor, or email the course coordinator to clarify the requirements. Real software projects have requirements that aren''t entirely clear, too! 

If necessary, there may be some small changes to the files that are provided, up to one week before the deadline, in order to make the requirements clearer, or to tweak test cases. These updates will be clearly announced on the Announcements page of Blackboard, and during the lectures. 

Hints:  1. It will be easier to implement the Section class first, followed by Location and then Track. The tests you

may wish to write before you start coding these classes.  2. Read the specification comments carefully. They have details that affect how you need to implement

test  We will try to use your test suite SectionTest to test an implementation of Section that contains some errors in an environment in which the other classes Section.java depends on exist and are correctly implemented. 

Marks for the JUnit4 test suite in SectionTest.java will be allocated as follows:  • Clear and systematic tests that can easily be used to detect most of the (valid) errors in a sample

implementation and does not erroneously find (invalid) errors in that implementation. Note: code submitted with compilation errors will result in zero marks in this section. A Java 8 compiler will be used to test code.