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Title: java-classes-in-mumbai-Abstract-data-type-chapter


1
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2
Abstract Data Types
Chapter 3
3
Data Structures
  • Data structure is a representation of data and
    the operations allowed on that data.

4
Abstract Data Types
  • In Object Oriented Programming data and the
    operations that manipulate that data are grouped
    together in classes
  • Abstract Data Types (ADTs) or data structures or
    collections store data and allow various
    operations on the data to access and change it

5
Why Abstract?
  • Specify the operations of the data structure and
    leave implementation details to later
  • in Java use an interface to specify operations
  • many, many different ADTs
  • picking the right one for the job is an important
    step in design
  • "Get your data structures correct first, and the
    rest of the program will write itself."           
        -Davids Johnson
  • High level languages often provide built in ADTs,
  • the C STL, the Java standard library

6
The Core Operations
  • Every Collection ADT should provide a way to
  • add an item
  • remove an item
  • find, retrieve, or access an item
  • Many, many more possibilities
  • is the collection empty
  • make the collection empty
  • give me a sub set of the collection
  • and on and on and on
  • Many different ways to implement these items each
    with associated costs and benefits

7
Implementing ADTs
  • when implementing an ADT the operations and
    behaviors are already specified
  • think Java interface
  • Implementers first choice is what to use as the
    internal storage container for the concrete data
    type
  • the internal storage container is used to hold
    the items in the collection
  • often an implementation of an ADT
  • initially slim pickings for choice of storage
    containers arrays anyone?

8
The Grand Tour
  • Why study ADTs?
  • Why reimplement some of them?
  • How many of you will actually go out and create
    your own linked list ADT from scratch?
  • Remember, the primary goal is to learn how to
    learn how to use and create ADTs
  • also learn the behavior of some of the more
    conventional ADTs

9
Bags and Sets
  • Simplest ADT is a Bag
  • items can be added, removed, accessed
  • no implied order to the items
  • duplicates allowed
  • Set
  • same as a bag, except duplicate elements not
    allowed
  • union, intersection, difference, subset

10
Lists
  • Items have a position in this Collection
  • Random access or not?
  • Array Lists
  • internal storage container is native array
  • Linked Lists
  • public class Node
  • private Object data
  • private Node next

last
first
11
Stacks
  • Collection with access only to the last element
    inserted
  • Last in first out
  • insert/push
  • remove/pop
  • top
  • make empty

Top
Data4
Data3
Data2
Data1
12
Queues
  • Collection with access only to the item that has
    been present the longest
  • Last in last out or first in first out
  • enqueue, dequeue, front
  • priority queues and deque

Front
Back
Data4
Data3
Data2
Data1
13
Stacks and Queues in the Java Collection API
  • No queue in the Java collections ADT
  • Stack extends Vector (which is almost exactly
    like ArrayList)
  • Hmmm?
  • One reason the Java Collections Library is often
    said to be broken
  • no Queue in Collection API

14
Trees
  • Similar to a linked list
  • public class TreeNode
  • private Object data
  • private TreeNode left
  • private TreeNode right

Root
15
Other Types of Trees
  • Binary Search Trees
  • sorted values
  • Heaps
  • sorted via a different algorithm
  • AVL and Red-Black Trees
  • binary search trees that stay balanced
  • Splay Trees
  • B Trees

16
HashTables
  • Take a key, apply function
  • f(key) hash value
  • store data or object based on hash value
  • Sorting O(N), access O(1) if a perfect hash
    function and enough memory for table
  • how deal with collisions?

17
The Java Collection Interface
  • boolean isEmpty()
  • int size()
  • boolean add(Object x)
  • boolean contains(Object x)
  • boolean remove(Object x)
  • void clear()
  • Object toArray()
  • Iterator iterator()

18
Generic Containers
  • ADTs or Collection classes should be generic
  • only write them once, hold lots or all types of
    data
  • Java achieves genericity through inheritance and
    polymorphism
  • ADTs have an internal storage container
  • What is storing the stuff,
  • implementation vs. abstraction
  • in Java, usually holds Objects. Why?

19
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20
Example - ArrayList
21
Thank You!!!
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