ELEC0021 Programming II 2018-19 Prof. G. Pavlou
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PROGRAMMING ASSIGNMENT 2
Ordered Linked List
In this programming exercise you are going to design, implement and test an ordered linked
list based on the generic List class introduced in the notes. The purpose of this exercise is to
understand in detail the use of inheritance through generic methods that are provided in
superclasses and can be used in diverse subclasses, resulting in reusability and extensibility. In
this specific case, generic find, insert and remove methods will be added to class OrderedList
(demonstrating reusability) and then could be used by specific subclasses, e.g. IntegerList,
StringList, etc., by introducing type-specific compare methods (demonstrating extensibility).
The class List introduced in the notes supports linked list functionality in terms of inserting
and retrieving elements to/from the front and back of the list only. But in some applications,
e.g. time-driven simulation of a real system, elements need to be inserted in the list keeping it
ordered, e.g. representing the time when an event will happen. In such a use of an ordered
linked list, elements are only retrieved from the front of the list, e.g. as time advances and the
first item in the list becomes the “current event”, and are inserted in the right place in the list
keeping it ordered. Another example is a list of student records ordered based on name.
So the first part of this exercise is to create an abstract class OrderedList class by extending
List and adding the following methods:
protected abstract int compare(Object obj1, Object obj2);
public ListNode find (Object newData) { /* to impl */ }
public boolean insert (Object newData) { /* to impl */ }
public ListNode remove (Object remData) { /* to impl */ }
The compare method does not know what types of objects to compare, as such it is abstract
making also OrderedList an abstract class. It is also protected as it is only used by this class
and derived classes.
The find method should “walk-through” the list, check to see if a ListNode with the same data
as newData exists by using compare and, if so, return it. The remove method should also
“walk” through the list to find the sought element, but if it exists it should remove and return
it. In order to do this we need to keep a reference to the previous element so that we are able
to link it with the element after the one to remove.
The insert method should also use compare to insert a new object in the list while keeping it
in order. It should check first using find if the element already exists to avoid duplicates. In
order to insert an element in-between two others, we need to have a reference to the previous
one and check if the element to insert is smaller than the next one, in which case it should be
inserted in-between the two. So a special “walk-though” the list is also required.
Note that by implementing the OrderedList through inheritance, we have the problem that the
List insertAtFront and insertAtBack methods can still be used while they should not! You
should redefine them to do nothing and just print a relevant error message.
Having now implemented OrderedList, you should implement a subclass IntegerOrdList
which should simply redefine the compare method. The redefined compare method should
also be protected and should now assume that the two objects are of type Integer, so the
arguments of type Object should be “casted back” to Integer, for example ((Integer)
obj1).intValue() returns the actual integer value in argument obj1. A negative result should
mean obj1<obj2, zero should mean obj1=obj2 and a positive result should mean obj1>obj2.
You should also provide constructors which should initialise the list and its name.
ELEC0021 Programming II 2018-19 Prof. G. Pavlou
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Having implemented the IntegerOrdList, you should also implement an IntegerOrdListTest
program that should demonstrate that the list works correctly. This should be done by getting
numbers from the user and inserting them. It should also support removal of a number the
user specifies. You should implement a small menu to guide the user through activities to add
a number, remove a number, print the list, etc.
The second part of this assignment will use exactly the same generic class infrastructure (List
and OrderedList) to implement a student record database in a similar fashion to last year’s C
assignment but without saving data to and retrieving them from a file. You should start by
introducing a StudentRecord class as follows:
public class StudentRecord {
public String surname;
public String name;
public int studentNo;
public float averageMark;
public String toString () // toString, implement
public StudentRecord (<parms>) // constructor, implement
}
You should also implement a StudentRecordOrdList which should be a very easy job given
that all the work is effectively done by OrderedList and you have already implemented
IntegerOrdList which is very similar (only the 1-line compare method will be different). For
the compare method, you should concatenate surname and name which together make the
student record unique.
Having implemented the StudentRecordOrdList, you should write a small program that allows
the user to introduce a student record (surname, name, number), remove a student record
(based on surname, name), include the average mark in a student’s record, find and print a
student’s record and finally print all students’ records. For the last feature, you may reimplement/overwrite
StudentRecordOrdList toString to print a record per line – the List
toString prints all elements in a single line. For this you may use the List getFirst method to
get a handle and walk through the data. (Note: you should treat the List as a Library class for
which you do not have access to its source code, hence you cannot change List toString).
You will realise that doing all this is very easy based on the generic object-oriented
infrastructure you created (i.e. List, OrderedList) which enables us to implement lists of any
content quickly and efficiently through reusability (we are reusing List and OrderedList) and
extensibility (we use inheritance to implement very easily StudentRecordOrdList).
You will be examined in the lab session of the 15 March, additional details will be provided
through moodle announcements. You should also submit at that time the following files:
OrderedList.java, IntegetOrdList.java, StudentRecordOrdList.java and the files of the two
programs implemented.
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