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COMP 121

COMP 121. Week 11: Linked Lists. Objectives. Understand how single-, double-, and circular-linked list data structures are implemented Understand the LinkedList class Understand the Iterator interface Understand the ListIterator interface

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COMP 121

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  1. COMP 121 Week 11: Linked Lists

  2. Objectives • Understand how single-, double-, and circular-linked list data structures are implemented • Understand the LinkedList class • Understand the Iterator interface • Understand the ListIterator interface • Become familiar with another piece of the Java Collection framework

  3. Linked Lists • Array List • The add and remove methods operate in linear time O(n) • Require a loop to shift elements in the underlying array • Linked List • Overcomes this by providing ability to add or remove items anywhere in the list in constant time O(1) • Each element (node) in a linked list stores information and a link to the next, and optionally previous, node Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  4. Single-Linked List Node • A node contains a data item and one or more links • A link is a reference to a node • A node is generally defined inside of another class, making it an inner class • The details of a node should be private Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  5. Single-Linked List Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  6. Add a Node in a Single-Linked List Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  7. Remove a Node from a Single-Linked List Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  8. Double-Linked Lists • Limitations of a single-linked list include: • Insertion at positions other than the first is O(n) • Insertion at the front of the list is O(1) • Can insert a node only after a referenced node • Can remove a node only if we have a reference to its predecessor node • Can traverse the list only in the forward direction • Limitations are overcome by adding a reference in each node to the previous node (double-linked list) Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  9. Double-Linked List Node Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  10. Double-Linked List Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  11. Add a Node to a Double-Linked List (Steps 1 and 2) Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  12. Add a Node to a Double-Linked List (Steps 3 and 4) Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  13. Remove a Node from a Double-Linked List Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  14. Circular Lists • Circular-linked list • Links the last node of a double-linked list to the first node and the first to the last • Advantages • Can traverse in forward or reverse direction even after you reach the last or first node • Can visit all list elements from any starting point • Can never fall off the end of a list • Disadvantage • Possibility of an infinite loop! Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  15. Circular Lists Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  16. The LinkedList<E> Class • Part of the Java API • Implements the List<E> interface using a double-linked list Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  17. The Iterator<E> Interface • The interface Iterator is defined as part of API package java.util • The List interface declares the method iterator(), which returns an Iterator object that will iterate over the elements of that list • An Iterator does not refer to or point to a particular node at any given time but points between nodes Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  18. The Iterator<E> Interface (cont’d) Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  19. The ListIterator<E> Interface • Iterator limitations • Can only traverse the List in the forward direction • Provides only a remove method • Must advance an iterator using your own loop if starting position is not at the beginning of the list • ListIterator<E> is an extension of the Iterator<E> interface that overcomes the above limitations • Like Iterator, a ListIterator should be thought of as being positioned between elements of the linked list Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  20. The ListIterator Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  21. The ListIterator Interface Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  22. LinkedList Methods that Return ListIterators Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  23. Comparison of Iterator and ListIterator • ListIterator is a subinterface of Iterator • Classes that implement ListIterator provide the capabilities of both • Iterator interface • Requires fewer methods • Iterates over more general data structures • Only in one direction (forward) • Iterator is required by Collection interface • ListIterator is required by List interface Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  24. Conversion between a ListIterator and an Index • The nextIndex method returns the index value of the item that would be returned by a call to the next method • The previousIndex method returns the index value of the item that would be returned by a call to the previous method • The listIterator(int index) method is a method in LinkedList • Returns a ListIterator whose next call to next() will return the item at position index Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  25. Project: Using a LinkedList • Develop a program to maintain a list of homework assignments. When an assignment is assigned, add it to the list, and when it is completed, remove it. Keep track of the due date. The program should provide the following services: • Add a new assignment • Remove an assignment • Provide a list of the assignments in the order they were assigned • Find the assignment with the earliest due date Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  26. HomeworkList theList Assignment add() remove() showAssignments() findEarliest() description dueDate compareTo() Class Diagram Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  27. HomeworkList Class import java.util.ListIterator; import java.util.LinkedList; public class HomeworkList { private LinkedList<Assignment> theList; public HomeworkList() { theList = new LinkedList<Assignment>(); } Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  28. HomeworkList Class (cont’d) public void add(Assignment assignment) { theList.addLast(assignment); } public void remove(Assignment assignment) { theList.remove(assignment); } Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  29. HomeworkList Class (cont’d) public void showAssignments() { String message; int i = 1; for (Assignment assignment : theList) { message = "Assignment #" + (i++) + ":\n" + assignment.getDescription() + "\nDue date: " + assignment.getDueDate(); System.out.println(message); } } Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  30. HomeworkList Class (cont’d) public Assignment findEarliest() { Assignment earliest = null; Assignment current; ListIterator<Assignment> iter = theList.listIterator(); if (iter.hasNext()) { earliest = iter.next(); while (iter.hasNext()) { current = iter.next(); if (current.compareTo(earliest) < 0) { earliest = current; } } } return earliest; } Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  31. Summary • A linked list consists of a set of nodes, each of which contains its data and a reference to the next node • To find an item at a position indicated by an index in a linked list requires traversing the list from the beginning until the item at the specified index is found Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  32. Summary (cont’d) • An iterator gives with the ability to access the items in a List sequentially • The ListIterator interface is an extension of the Iterator interface • The Java API provides the LinkedList class, which uses a double-linked list to implement the List interface Koffman, E.B. & Wolfgang, P.A.T. (2003). Objects, Abstraction, Data Structures, and Design Using Java Version 5.0. New York: John Wiley & Sons.

  33. Any Questions?

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