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Stacks and Queues

Stacks and Queues. What is a Data Structure?. A data structure is a type of data storage ….similar to an array. There are many data structures in Java (Stacks, Queues, LinkedList, Sets, Maps, HashTables, Trees). Our discussion of data structures will be limited to Stacks and Queues.

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Stacks and Queues

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  1. Stacks and Queues

  2. What is a Data Structure? • A data structure is a type of data storage ….similar to an array. • There are many data structures in Java (Stacks, Queues, LinkedList, Sets, Maps, HashTables, Trees). • Our discussion of data structures will be limited to Stacks and Queues.

  3. Stacks and Queues • Stack: collection of items with "last in first out" retrieval • Queue: collection of items with "first in first out" retrieval

  4. Stacks • A data structure for maintaining data. Data goes in and out of the "top." • Has a specific set of operations that can be performed on the data. • Referred to as a LIFO data structure because of the last-in, first-out organization. • Implemented as a class. An array is one way to store the data.

  5. Stacks • Allows insertion and removal of elements only at one end • Traditionally called the top of the stack • New items are added to the top of the stack • Items are removed at the top of the stack • Called last in, first out or LIFO order • Traditionally, addition and removal operations are called push and pop • Think of a stack of books

  6. A Stack of Books

  7. Stacks Methods top: Returns the last value added to the stack pop: Removes and returns the last value added to the stack push: Adds an item to the top of the stack isEmpty: Returns true when there are no items on the stack size: Returns the number of items on the stack makeEmpty: Removes all the items on the stack

  8. Queues • Add items to one end of the queue (the tail) • Remove items from the other end of the queue (the head) • Queues store items in a first in, first out or FIFO fashion • Items are removed in the same order in which they have been added • Think of people lining up • People join the tail of the queue and wait until they have reached the head of the queue

  9. Queues • A data structure for maintaining data. Data goes in the "rear" and out the "front." • Has a specific set of operations that can be performed on the data. • Referred to as a FIFO data structure because of the First-in, first-out organization. • Implemented as a class. An array is one way to store the data.

  10. Queue Methods front: Returns the first value added to the queue dequeue: Removes and returns the first value added to the queue enqueue: Adds an item to the rear of the queue isEmpty: Returns true when there are no items in the queue size: Returns the number of items in the queue makeEmpty: Removes all the items in the queue

  11. Queues Figure 13:A Queue

  12. Stacks and Queues • Queue • Event queue of all events, kept by the Java GUI system • Queue of print jobs • Stack • Run-time stack that a processor or virtual machine keeps to organize the variables of nested methods

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