Generics and Collections in Java

As we discussed in the lectures, Java has a very structured Collections library. We can develop a similar simplified library for Java that uses arrays underneath. We will implement some the interfaces some abstract class, some concrete classes, and some of the helper classes such as iterators.



















The above figure shows a simplified version of the Collections. We will write corresponding generic classes for Collection, Set, List, Queue, which are all interfaces. HashSet, ArrayList, and LinkedList are concrete classes. Note that LinkedList uses multiple inheritance. Following table defines the functions for each class

Class Name
Public Method Name
Definition
Collection
This is a generic class with one generic parameters  which is the generic type E.

iterator()
Returns an iterator over the collection







add(E e)
Ensures that this collection contains the specified element







addAll(Collection c)
Adds all of the elements in the specified collection to this





collection

clear()
Removes all of the elements from this collection







contains(E e)
Returns true if this collection contains the specified element.







containsAll(Collection c)
Returns true if this collection contains all of the elements in the





specified collection.

isEmpty()
Returns true if this collection contains no elements.







remove(E e)
Removes a single instance of the specified element from this





collection, if it is present

removeAll(Collection c)
Removes all of this collection's elements that are also contained





in the specified collection


retainAll(Collection c)
Retains only the elements in this collection that are contained in





the specified collection

size()
Returns the number of elements in this collection.



Set
A collection that contains no duplicate elements. There is no order for this collection. In other

words, you don’t have to keep the insertion order of the elements.
List
An ordered collection (also known as a sequence). The user of this interface has precise

control over where in the list each element is inserted.
Queue
Queues order elements in a FIFO (first-in-first-out) manner. There is no random access with

this Collection. Some functions throw exceptions.

add(E e)
Inserts the specified element into this queue

element()
Retrieves, but does not remove, the head of this queue.

offer(E e)
Inserts the specified element into this queue

poll()
Retrieves and removes the head of this queue, or throws if this


queue is empty.
HashSet
Implements Set functions

ArrayList
Implements List functions

LinkedList
Implements both List and Queue functions. Your class does not have to have a linked list to

implement these.

Iterator
hasNext()
Returns true if the iteration has more elements.

next()
Returns the next element in the iteration and advances the


iterator.

remove()
Removes from the underlying collection the last element returned


by this iterator

Your Java Collections hierarchy should use only Java arrays in the concrete classes to implement all the methods.

You will test each method of each concrete class with generic parameters of int and string.

Notes:

    • Do error and range checking for any parameters. Throw exceptions and test them in your client code. Do not forget to define the throw lists for your functions.

    • For each class you will write appropriate class documentation for Javadoc. You will also submit the Javadoc files.

    • As expected, you should follow all object-oriented programming principles.

    • You should submit your work to the moodle page.

    • You should submit the images of drawn shapes.