1. Introduction to Objects and Encapsulation Computer Science 4 Mr. Gerb Reference: Objective: Understand Encapsulation and abstract data types

2. Object-Oriented Programming Became popular in the 1980s –We used to see programs as sequences of steps –OOP sees them as collections of objects and operations on those objects. Object-Oriented Languages –Smalltalk (one of the first) –C++ (still the most popular) –Java (one of the most recent)

3. What is an Object-Oriented Language? Allows the user to define objects –Objects contain data –Objects contain operations called methods to manipulate that data Supports three capabilities: –Encapsulation - Can offer users objects and methods without providing access to underlying data. –Polymorphism - Objects can define their own behavior for a method. –Inheritance - Can create subclasses with all the methods and data of their superclasses. We will discuss polymorphism and inheritance later

4. Why is encapsulation important? Supports data abstraction - The separation of a data type’s operations (what it can do) from its implementation (how it does it). Can change the way a data structure is implemented without affecting its users –To improve efficiency, for example –There may be thousands of users

5. For example - Your library Defined by its operations –Checkout/checkin a book –Pay an overdue fine Library can change the computer program it uses to store what books are checked out –You might not know it –The operations above stay the same

6. Abstract Data Type vs. Data Structure An abstract data type is defined by its interface –Specifies which operations it offers. –Does not specify how its data is stored –Also does not specify how the operations work. Data structure –How an abstract data type is implemented –Specifies how the data is stored –Specifies how the operations are implemented

7. Encapsulation and OOP in Java Objects –Programmers define classes Abstract data types –Public methods –Parameter and return types Data structures and implementation –Private data –Body of public methods –Private methods

8. Example: Strings Abstract type –Create a string –Concatenate two strings –Find a substring –Compare two strings Data Structure / Implementation –Contiguous 1 byte storage cells? (I guess...) –I don’t need to know that to use strings.

9. We will study data types in two steps 1.Define an abstract data type (ADT) 2.Study the various data structures that can be used to implement them. Some ADTs we will study: Unsorted lists, sorted lists, stacks, queues, priority queues, sets and maps Some data structures we will study: Arrays, linked lists, binary trees, hash tables, heaps

10. Types of operations on an abstract data type Constructor - Makes an instance of the ADT Observer - (a.k.a. accessors) Gives info about the state of the ADT Modifier- (a.k.a. mutators or transformers) change the state of ADT Iterators - Allows the components of the ADT to be processed in a sequence

11. An ADT for a School Schedule Operations (which type are each?): –Start a new school year –Create a new class –Enroll a student –Add a student to a class –Tell whether a student is in a class –Tell whether a class is full –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

12. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class –Enroll a student –Add a student to a class –Tell whether a student is in a class –Tell whether a class is full –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

13. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student –Add a student to a class –Tell whether a student is in a class –Tell whether a class is full –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

14. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class –Tell whether a student is in a class –Tell whether a class is full –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

15. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class - Modifier –Tell whether a student is in a class –Tell whether a class is full –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

16. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class - Modifier –Tell whether a student is in a class - Observer –Tell whether a class is full –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

17. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class - Modifier –Tell whether a student is in a class - Observer –Tell whether a class is full - Observer –Drop a student from a class –Alphabetical listing of all students –List of all classes offered

18. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class - Modifier –Tell whether a student is in a class - Observer –Tell whether a class is full - Observer –Drop a student from a class - Modifier –Alphabetical listing of all students –List of all classes offered

19. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class - Modifier –Tell whether a student is in a class - Observer –Tell whether a class is full - Observer –Drop a student from a class - Modifier –Alphabetical listing of all students - Iterator –List of all classes offered

20. An ADT for a School Schedule Operations (which type are each?): –Start a new school year - Constructor –Create a new class - Modifier –Enroll a student - Modifier –Add a student to a class - Modifier –Tell whether a student is in a class - Observer –Tell whether a class is full - Observer –Drop a student from a class - Modifier –Alphabetical listing of all students - Iterator –List of all classes offered - Iterator

21. Summary Object-oriented languages support encapsulation, polymorphism and inheritance Encapsulation supports data abstraction Two levels of data types –Abstract data types - Operations –Data structures - Storage and implementation Types of operations: Constructors, observers, modifiers, iterators