Array-Based Implementations

1. Array-Based Implementations Chapter 3

2. The Approach • An ADT is • A collection of data … and … • A set of operations on that data • Specifications indicate • What ADT operations do • But not how to implement • First step for implementation • Choose data structure

3. Poor ADT Design • Violating the wall of ADT operations by allowing client program to access data members of class directly.

4. Core Methods • Poor approach • Define entire class and attempt to test • Better plan – Identify, then test basic (core) methods • Typical core methods • Create the container (constructors) • Setters • Getters • Add items • Display/list items • Remove items

5. Using Fixed-Size Arrays • Must keep track of array elements used, available • Consider if the add method places elements in consecutive positions of array • What happens when add method has used up final available position? • Where can elements be removed? • What happens when last element is removed?

6. Array-Based Implementation of ADT Sack • Core ArraySack methods • +getCurrentSize(): integer • + isEmpty(): boolean • +add(item: T): boolean • +remove(item: T): boolean • +clear(): void • +contains(item: T) :boolean Also; Constructors (plus copy), assignment operator, destructor, iostream operator overloads.

7. Array-Based Implementation of ADT Sack • An array-based implementation of the ADT sack

8. SackInterface – Chapter 3 • Template class – supports generics, the class collection may hold any valid C++ type/class. • All methods are virtual allowing the derived class to override the method, thus late binding occurs at execution time not compile time – which method to call – the child’s or parent’s? • All methods are abstract = 0, no bodies meaning the class can not be instantiated, no objects of the class can be created. • The class is a pure abstract class, abstract if at least one method is virtual with an empty body, pure because all methods are defined as such (except destructor). • The class interface is used for inheritance of specification – all derived classes of the interface must include the interface methods.

9. ArraySack ADT • The header file for the class ArraySack • Code for header and implementation are available on lecture page of class web site • Notice use of template parameter T • Notice use of inheritance; ArraySack is a child class of the SackInterface class • Inheritance is “public” – everything that is public in Base class is public in Derived class • Go over method specifications and data member declarations

10. Defining the Core Methods • Go over method implementations

11. Defining the Core Methods • Inserting a new entry into an array-based sack

12. Methods That Remove Entries • The array items after a successful search for the string "Alice"

13. Methods That Remove Entries • A gap in the array items after the entry in items[index] is removed and decrementing itemCount;

14. Methods That Remove Entries • Could shift subsequent entries to avoid a gap as in figure or simply copy last entry into gap (as in next slide)

15. Methods That Remove Entries • Avoiding a gap in the array while removing an entry

16. Testing the Core Methods • Go over main implementation

17. End Chapter 3