1. Chapter 10 Thinking in Objects
Dr. Clincy

2. Structured or Procedural Programming Versus OO Programming
Structured Programming Languages
Fortran
Pascal
Ada C
BASIC
Description: Procedural approach tackles a specific problem upfront – build exactly what is needed to solve the problem, focus on using the specific data needed and in designing and implementing the needed subroutines and functions (or “methods” in using an OOP term) – focuses on specific data and methods.
Object-Oriented Programming Languages
Java
Python
Ruby C#
C++
Visual Basic
Description (Student): The initial step is to design and build classes and their operations (i.e. methods) with no real focus on a specific problem. The second step is to use the derived objects and their methods and data to solve some specific problem. In addition to a focus on data and methods in general, also focuses on “Classes and Objects”
Description (Professional): The 1st step is to look for existing classes and objects that can be used to solve some specific problem. If no luck, determine which existing classes and objects can be altered. If no luck, build new classes and objects.
Dr. Clincy

3. Structured or Procedural Programming Versus OO Programming
Focuses on designing methods
Data and operations on the data are separated
Data must be passed to the methods
Programs are more abstract and catered for a specific problem/use/etc..
Code reuse is not suitable
Involves thinking in terms of specific methods and data
Object-Oriented Programming
Couples data and methods into objects
Programs mirror real world
Languages are built to easy allow objects to have associated attributes and activities
Code reuse is suitable
Involves thinking in terms of objects (and classes)
Btw: encompasses structured programming with an added dimension that integrates data with operation into objects
Dr. Clincy

4. Class Abstraction and Encapsulation
Class abstraction means to separate class implementation from the use of the class.
The creator of the class provides a description of the class and let the user know how the class can be used.
The user of the class does not need to know how the class is implemented. The detail of implementation is encapsulated and hidden from the user.
A description and collection of public constructors, methods, and field that are accessible from outside the class is called the Class’s Contract
Encapsulation
For OOP, it is really all about understanding Class’s Contract in not re-inventing the wheel
Explain OOL to high-level language to low-level language concept
Dr. Clincy

5. Example: Building a Car from a OOP Perspective
Car has many components such as carburetor, starter, alternator, engine, AC system, gas tank, transmission system, etc
Each component can be viewed as an object that has properties and methods
To get the components to work together, you only need to know how the component is used and how it interacts with one another (abstraction) – OOP way of Thinking
You don’t need to know how each component works internally – you can build the car without knowing (encapsulation).
Dr. Clincy

6. Class Relationships
In designing classes, you must first explore the relationships among classes.
COMMON CLASS RELATIONSHIPS
Association – a general binary relationship that describes an activity between two classes
Aggregation – an association that represents an ownership relationship between two objects
Composition – an association that represents an “exclusive” ownership relationship between two objects
Inheritance – the ability to generate a specialized class (subclass) from a general class (superclass). Will cover this in a later chapter.
Dr. Clincy

7. Association – UML Example
Association – a general binary relationship that describes an activity between two classes
A Faculty member teaching a course is an association between the Faculty Class and the Course Class
A Student taking a Course is an association between the Student Class and the Course Class
Relationship’s “label” and the relationship’s direction
Relationship’s “label” and the relationship’s direction
Student
Role name that describes role in relationship
A course is taught by only one faculty member
A course may have 5 to 60 students
A student may take any number of courses
A faculty may at most 3 courses
Dr. Clincy

8. Association – Implementation
The association relations are implemented using data field and methods in classes.
The Faculty-Teaches-A-Course relationship is implemented using addCourse method in Faculty class and setFaculty method in the Course class
The Student-Taking-A-Course relationship is implemented using addCourse method in Student class and addStudent method in the Course class
The Faculty class can use a list to store the courses the faculty is teaching
The Student class can store a list of courses the student is taking
The Course class can use a list to store the students taking the course
The Course class can use a data field to store the faculty who teaches the course
Dr. Clincy

9. Aggregation and Composition
Aggregation – an association that represents an ownership relationship between two objects
Owner object is called the “aggregating object” and it’s class is called the “aggregating class”
Subject object is called the “aggregated object” and it’s class is called the “aggregated class”
Name
Student
Address
If the subject object CAN NOT exist without the Owner object, this aggregation is called “Composition”
Name cannot exist without Student
Address CAN exist without Student
Up to 3 students can share the same address
Dr. Clincy

10. Aggregation and Composition - Implementation
The Student-Has-A-Name relationship is implemented using the data field “name” in the Student class – the aggregating class
The Student-Has-An-Address relationship is implemented using the data field “name” in the Student class – the aggregating class
NOTE: Since aggregation and composition relationships are represented using classes in similar ways, many textbooks don’t differentiate them and call both compositions.
Dr. Clincy

11. Aggregation Between Same Class
Aggregation may exist between objects of the same class. For example, a person may have a supervisor.
public class Person {
// The type for the data is the class itself
private Person supervisor;
... }
The Person-Has-A-Supervisor relationship implementation
What happens if a person has several supervisors?
Can use an array to implement the Person-Has-Many-Supervisors relationship
Dr. Clincy

12. Wrapper Classes Boolean Integer Character Long Short Float Byte Double
Primitive data types (ie. Bool, Char, Int, Byte, etc) are NOT treated like objects – for performance and efficiency reasons
However, many Java methods require the use of objects as arguments
Java provides the ability to incorporate or “wrap” a primitive data type value into an object – wrapper class
Java provides the following wrapper classes via it’s java.lang package:
Boolean
Character
Short
Byte
Integer
Long
Float
Double
NOTE: (1) The wrapper classes do not have no-arg constructors. (2) The instances of all wrapper classes are immutable, i.e., their internal values cannot be changed once the objects are created.
Dr. Clincy

13. We will cover the String class in the next lecture.
Let’s review and start Lab 2
Dr. Clincy