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Chapter 3 List Stacks and Queues Data Structures Data structure is a representation of data and the operations allowed on that data. 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 The Core Operations Every Collection ADT should provide a way to: Many, many more possibilities add an item remove an item find, retrieve, or access an item 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 Implementing ADTs when implementing an ADT the operations and behaviors are already specified think Java interface Implementer’s 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? 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 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 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; } first last Stacks Collection with access only to the last element inserted Top Last in first out Data4 insert/push Data3 remove/pop Data2 top Data1 make empty 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 Data1 Back Data2 Data3 Data4 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 Trees Similar to a linked list public class TreeNode { private Object data; private TreeNode left; private TreeNode right; } Root Other Types of Trees Binary Search Trees Heaps sorted via a different algorithm AVL and Red-Black Trees sorted values binary search trees that stay balanced Splay Trees B Trees 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? Other ADTs Maps a.k.a. Dictionary Collection of items with a key and associated values similar to hash tables, and hash tables often used to implement Maps Graphs Nodes with unlimited connections between other nodes Sparse vectors and sparse matrices 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() Interface????? 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? java.util Example - ArrayList Class ArrayList java.lang.Object | +--java.util.AbstractCollection | +--java.util.AbstractList | +--java.util.ArrayList All Implemented Interfaces: Cloneable, Collection, List, Serializable void add(int index, Object element) Inserts the specified element at the specified position in this list. boolean add(Object o) Appends the specified element to the end of this list. void clear() Removes all of the elements from this list. boolean contains(Object elem) Returns true if this list contains the specified element. int indexOf(Object elem) Searches for the first occurence of the given argument, testing for equality using the equals method. boolean isEmpty() Tests if this list has no elements. Object set(int index, Object element) Replaces the element at the specified position in this list with the specified element. int size() Returns the number of elements in this list.