HIT2037- HIT6037 Software Development in Java 22 – Data Structures and Introduction

2 Content Introduction to data structures Introduction to sorting Introduction to searching

3 What is a Data Structure? We have already worked out how to store objects in an ArrayList However, there are other “Data Structures” that allow us to store collections of objects Each structure has different strengths and weaknesses One structure might be perfect for one application and terrible for another

4 Linked List “ A link list has a number of nodes each of which has a reference to the next node” [1] Key features  Good where items need to be removed or added in the middle of the list ( just change the reference)  Sequential access is efficient  Java provides a LinkedList in the util package  LinkedList  An iterator can be used with a LinkedList  See simulation

5 Linked List – Some Operations addLast(E e) addFirst(E e) add(int index, E element) getFirst() getLast() indexOf(Object o) peekFirst() peekLast() Other data structures such as Stacks and Queues are often based on Linked Lists Linked Lists do not do this efficiently. They only allow sequential access Items in the list do not need to be stored in order in memory Variations include Circular lists, link from head to tail Double linked lists, traverse forward and backwards

6 Queue Implements “first in first out” Example “a queue of jobs to do” Java provides a Queue class in the util package Important operations  add (E e) // returns true if it works  poll() // retrieves head or returns false (check this)  peek() // retrieves head but does not remove  remove() // retrieves and removes head of queue Why use it? “Conceptually what we want”[2] A pipe Items you want to deal with order of arrival (Time?)

7 Stack Implements “last in first out” “What does the stack do in the computers memory?” Java provides a Stack class in the util package Important operations  push (E e) // add item to the stack  pop() // take item off the top of the stack  peek() //get without removing  empty() // see if stack is empty  search(Object o) // returns position of object in stack Its interesting to note this class inherits from Vector Why use a stack, Good for reversing a series of operations Open 1 open 2 open 3 Now go back, undo [3]

8 Hash Table, (from the api) “This class implements a hashtable, which maps keys to values. Any non-null object can be used as a key or as a value.”

9 References [1] Cay Horstmann, Java Concepts, 5 th Edition, [2], [3],