Java Tutorial Lab 7

LAB #7
Prepared by: Berk Soysal
2016 Winter

ArrayQueueLinkedListVectorArrayList
Java comes with a group of generic collection classes that grow as more
elements are added to them. This group of collection classes are referred to
as the Java Collections Framework.
2016 Winter

• The Set interface defines the methods required to process a
collection of objects in which there is no repetition, and
ordering is unimportant.
• Which of these are sets?
– a queue of people waiting to see a doctor;
– a list of number one records for each of the 52 weeks of a particular
year;
– car registration numbers allocated parking permits.
• There are three implementations provided for the Set
interface in the JCF ( Java Collections Framework).
• They are HashSet, LinkedHashSet and TreeSet.
• Only the collection of car registration numbers can be
considered a set as there will be no duplicates and ordering
is unimportant.
2016 Winter

ArrayList LinkedList
1) ArrayList internally uses dynamic
array to store the elements.
LinkedList internally uses doubly
linked list to store the elements.
2) Manipulation with ArrayList is
slow because it internally uses
arrays. If any element is removed
from the array, all the bits are
shifted in memory.
Manipulation with LinkedList is
faster than ArrayList because it uses
doubly linked list so no bit shifting is
required in memory.
3) ArrayList class can act as a list
only because it implements List only.
LinkedList class can act as a list and
queue both because it implements
List and Deque interfaces.
4) ArrayList is better for storing and
accessing data(reading).
LinkedList is better for manipulating
data.
2016 Winter

• The List interface specifies the methods required to process an
ordered list of objects.
• Such a list may contain duplicates.
Examples of a list of objects:
• Jobs waiting for a printer,
• Emergency calls waiting for an ambulance
• The names of players that have won the Wimbledon tennis
tournament over the last 10 years.
• We often think of such a collection as a sequence of objects.
• There are three implementations provided for the List interface
in the JCF.
• They are ArrayList, Vector (Not preferred) and LinkedList.
2016 Winter

• Queue: Retrieves elements in the order they were added.
• First-In, First-Out ("FIFO")
• Elements are stored in order of
insertion but don't have indexes.
• Client can only add to the end of the
queue, and can only examine/remove
the front of the queue.
• Basic queue operations:
– add (enqueue): Add an element to the back.
– remove (dequeue): Remove the front element.
– peek: Examine the front element.
2016 Winter

• Just like Stacks, Queues can be implemented by using two
families of implementations:
 Array-based implementation
 LinkedList-based implementation
2016 Winter

• The first implementation stores the underlying collection in a
fixed-sized array.
2016 Winter

• The second implementation uses a linked-list to store the
queue’s contents. Using such an approach provides a very
efficient, succinct implementation with low computation
complexity.
2016 Winter

• Each element (node) of a list comprises of two items - the
data and a reference to the next node.
• The last node has a reference to null.
• The entry point into a linked list is called the head of the list.
It should be noted that head is not a separate node, but the
reference to the first node. If the list is empty then the head
is a null reference.
Figure - Singly Linked List
2016 Winter

• A doubly linked list is a list that has two references, one to
the next node and another to previous node.
Figure – A Doubly Linked List
• Another important type of a linked list is called a circular linked list
where last node of the list points back to the first node (or the head)
of the list.
2016 Winter

For this laboratory, we are developing a computer simulation
for a supermarket that has express and regular lines. These
waiting lines will be implemented with help of queues.
2016 Winter

As you can see, the average waiting time for the
express line was short (16 seconds!) but the
customers in the regular line are waiting more than
30 minutes. The manager needs to add regular lines.
But how many lines should be added? To answer this
question, you will need to modify this application to
allow for more regular lines;
2016 Winter

Please take a look at the code provided in the folder;
Lab7 -> Queue Implementations -> LinkedList Queues ->…
2016 Winter

Java Tutorial Lab 7

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