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Understanding Queues in Data Structures: Enqueue, Dequeue, and Implementation Techniques

This chapter discusses the fundamentals of queues in data structures, detailing their operations such as enqueue, dequeue, and getFront, all of which execute in constant time. Emphasizing the First-In-First-Out (FIFO) principle, it explores typical applications including process queues in operating systems and event-driven simulations. Implementations of queues are covered, both using arrays and linked lists, alongside an overview of double-ended queues (deques). This comprehensive guide serves as a critical resource for understanding and implementing queues in Java.

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Understanding Queues in Data Structures: Enqueue, Dequeue, and Implementation Techniques

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  1. Chapter6.6, 16+ 13.2 (event-driven simulation) Queues CSCI 3333 Data Structures

  2. Outline • Intro. to Queues • java.util.Queue interface • Example programs CSCI 3333 Data Structures

  3. Queue • Typical application of Queue: A collection designed for holding elements prior to processing. • Supported operations: • enqueue (n): add n at the back of the queue • dequeue( ): remove the object at the front /head of the queue and return that object • getFront( ): aka. element( ), peek( ) return the object at the front of the queue (w/o removing it from the queue) • All three operations take constant time. CSCI 3333 Data Structures

  4. Queues • Special features: (typically) First in, first out (FIFO) - dequeue( ) and getFront( ) returns the least recently added item in the queue. Exceptions: priority queues Items in a priority queue are ordered according to some criteria (example: in OS, types of the processes, user privileges, etc.) CSCI 3333 Data Structures

  5. Applications of Queue • In any computer applications that need to deal with a waiting list of something. e.g., In operating systems: A process queue collects processes that are waiting to use the processor or other system resources. e.g., In event-driven simulation: A priority queue stores the list of events that need to be handled by the simulator. e.g., ? CSCI 3333 Data Structures

  6. Implementation of Queue • A Queue may be implemented as an Array or a Linked List. • as a dynamic array: • ArrayQueue.java(Figure 16.8 – 16.17) private AnyType [ ] theArray; private int currentSize; private int front; private int back; private static final int DEFAULT_CAPACITY = 10; CSCI 3333 Data Structures

  7. CSCI 3333 Data Structures

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  9. Implementation of Queue • as a linked list: • ListQueue.java (Figure 16.23 – 16.27) See http://sce.uhcl.edu/yang/teaching/JavaProgrammingExamplesandRelatedTopics.htm#queues for an example testing program. CSCI 3333 Data Structures

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  11. Interface: java.util.Queue http://download.oracle.com/javase/6/docs/api/java/util/Queue.html Interface Queue<E> CSCI 3333 Data Structures

  12. Array-based queues vs LinkedList-based queues CSCI 3333 Data Structures

  13. Double-Ended Queues (deque) • A queue that allows access at both ends. Enqueue addFront, addRear Dequeue  removeFront, removeRear • In Java: • java.util.Deque interface http://download.oracle.com/javase/6/docs/api/java/util/Deque.html • Class ArrayDeque<E> http://download.oracle.com/javase/6/docs/api/java/util/ArrayDeque.html • The LinkedListclass can be used as a stack, queue, or deque, because it implements both the List and the Deque interfaces. • http://en.wikipedia.org/wiki/Double-ended_queue CSCI 3333 Data Structures

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