1. CSC 212 – Data Structures Lecture 13: Linked Lists

2. Classes Every class & interface must be in own file  File should have name of class/interface  Files should be in same directory Subclass extends its superclass  Extends exactly 1 class Subclass inherits methods & fields  Makes no difference if inherited from superclass’s superclass  Can use all that are not private

3. Interfaces Interfaces create 2 nd mode of inheritance  Can only declare public abstract methods  Provides “contract” of functionality Classes implement interfaces  Can implement any number of interfaces  Must have definition for all interface methods  Automatically include interfaces implemented by superclasses Get more used to these as we continue…

4. Arrays Nice for simple storage & retrieval of data  Bad when moving data around  Ever try to resize an array?  Guess too small and program cannot run  Guess too large and memory wasted

5. Performance at Limited Memory

6. Better Option Solve this problem using linked lists  Implementation that grows & shrinks with data  Also our first recursive structure Many implementations of linked list  Which one is best? Depends on situation  Each has own strengths & weaknesses  This will be a recurring refrain for this class Important to understand how each works

7. Singly Linked List A singly linked list is sequence of nodes Node contains  element  reference to next Node elem node Singly Linked List With 4 Elements ABCD  next

8. Our First (Not Last) Node Class public class Node { private String element; private Node next; public Node() { this(null, null); } public Node(String e, Node n) { element = e; next = n; } public String getElement() { return element; } public Node getNext() { return next; } public void setElement(String newE) { element = newE; } public void setNext(Node newNext) { next = newNext; } }

9. Singly Linked List public class SList { private Node head; // head is null  list is empty // else head references 1 st Node in list // Could add size field, but why?... // Methods go here, but don’t want to ruin // your “fun” }

10. Inserting at Head 1. Allocate new node 2. New node’s next field alias old head 3. Alias head to new node Done! BCD  head BCD  A BCD  A

11. Removing a Node 1. Find node before target in list 2. If target not the head a) Node’s next field alias target’s next 3. Else a) Reassign head Done! BCD  head A trav BCD  head A trav

12. Doubly Linked List DNode subclass of Node; adds prev field DList is not subclass of List  Defines identical methods…  …all of which need to be redefined Now, let’s have some volunteers…

13. Circular Linked List Nodes identical to doubly linked list Big difference  last node contains reference to first Notice this becomes a big circle  Now you know the idea behind the name BCD head A

14. Before Next Lecture… Do week #5 assignment Continue programming assignment #1  It is due Friday Start reviewing for Midterm #1  It will be on Monday Fridays’s lecture introduces recursion  Read Section 3.5 of the book  If you don’t read, you won’t understand, and I don’t care