C SC 205 Lecture 10: Singly-Linked Lists
major resources: Data Structures and the Java Collections Framework Second Edition, William Collins, McGraw-Hill, 2005
Introduction to Programming and OO Design using Java, Niño and Hosch, Wiley & Sons, 2002

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Monday October 22 (week 7)

Linked list concept

• Each list entry created independently
• Each list entry explicitly linked to the next (and possibly previous) entry
• Access is inherently sequential, not direct
• We've already considered time efficiency of major operations
• Space efficient in the sense that no space is wasted (compared to array-based list)
• Space inefficient in the sense that each entry requires at least one reference as overhead
• Generic singly-linked list structure diagrammed

SinglyLinkedList class specification

• Developed for textbook
• Not part of Java Collections Framework
• Extends AbstractCollection
• Implements Iterable, Collection, and List

SinglyLinkedList class implementation

• As the name implies, is implemented using singly-linked list
• due to its rich heritage of super abstract classes and interfaces, it is obliged to define a large number of methods!
• Most methods are defined to simply throw UnsupportedOperationException
• Note use of inner class for Entry data structure. Each Entry object has reference to a list element and a reference to the next list Entry.
• We studied the source code for a few methods
• public SinglyLinkedList()
• public int size()
• public boolean isEmpty()
• public boolean contains(Object) (note that null elements are allowed, use of == and equals())
• public boolean add(E)
• Studied the inner class to implement its iterator

Inner class SinglyLinkedListIterator

• Is there any difference between an inner class and a nested class?
• Why define this as an inner class?
• Iterators and the Factory Pattern (design patterns are a topic for CSC 225)
• The iterator concept
• It maintains a pointer that rests between entries
• Initially to the left of first entry
• next() will advance it beyond the next entry and returns it
• hasNext() will be false after it advances past the last entry
• Thus you have to call next() to access the first element
• One-way iteration from beginning to end
• This class implements Iterator
• Obliged to define the boolean hasNext(), E next() and void remove() methods
• Also defines a constructor, but allows remove() to throw UnSupportedOperationException