1. Chapter 10 Thinking in Objects Part 1

2. Class Abstraction & 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
Example: The use of a PC does not require the knowledge of its internal workings

3. Example: The Loan Class
A specific loan can be viewed as an object of a Loan class. The interest rate, amount, and period are its properties, and computing the monthly & total payments are its methods. When you buy a car, a loan object is created by instantiating the class with your loan interest rate, amount, and period. You can then use the methods to find the monthly & total payments. As a user of the Loan class, you don’t need to know how these methods are implemented
Example: The Loan Class
Loan
TestLoanClass
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4. Object-Oriented Thinking
Chapters 1-8 introduced fundamental programming techniques for problem solving using loops, methods, and arrays. The studies of these techniques lay a solid foundation for object- oriented programming
Classes provide more flexibility and modularity for building reusable software. This section improves the solution for a problem introduced in Chapter 3 using the object-oriented approach
From the improvements, you will gain the insight on the differences between the procedural programming and object- oriented programming and see the benefits of developing reusable code using objects and classes

5. Example: The BMI Class BMI UseBMIClass
In procedural programming, data & operations on the data are separate. It requires passing data to methods. The OO approach mirrors the real world, in which objects are associated with both data & operations. Using objects improves reusability, making programs easier to develop and maintain. An OO program can be viewed as a collection of cooperating objects. This example is an OO version of the procedural program of Listing 3.4
Example: The BMI Class
BMI
UseBMIClass
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6. Class Relationships Association Aggregation Composition Inheritance
Association is a general binary relationship that describes an activity between two classes

7. Aggregation Composition
A "uses" B. B exists independently (conceptually) from A
Example: A Company is an aggregation of People
A Company is a composition of Accounts
When a Company ceases to do business its Accounts cease to exist but its People continue to exist
Composition
A "owns" B. B has no meaning or purpose in the system without A
Example: A Text Editor owns a Buffer (composition)
A Text Editor uses a File (aggregation)
When Text Editor is closes, the Buffer is destroyed but the File is not
Source: programmers.stackexchange.com/questions/61376/aggregation-vs-composition/61527#61527

8. Aggregation & Composition
Composition is actually a special case of the aggregation relationship
Aggregation models has-a relationships and represents an ownership relationship between two objects
The owner object is called an aggregating object and its class an aggregating class. The subject object is called an aggregated object and its class an aggregated class

9. Aggregation & Composition
An aggregation relationship is represented as a data field in the aggregating class

10. Aggregation Between Same Class
Aggregation may exist between objects of the same class
public class Person {
// The type for the data is the class itself
private Person supervisor;
... }

11. Aggregation Between Same Class
What happens if a person has several supervisors?

12. Example: The Course Class
The Course class encapsulates the internal implementation. The user can create a Course object and manipulate it through the public methods addStudent, dropStudent, getNumOfStudents and getStudents. However, the user doesn’t need to know how these methods are implemented
This example uses an array to store students, but you could use a different data structure to store students. The program that uses Course does not need to change as long as the contract of the public methods remains unchanged
Course
TestCourse
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13. Source: https://www.youtube.com/watch?v=CgFVgp_VCN8
Stack in Motion
Source:

14. Example: Stack of Integers

15. Stack of Integers

16. The StackOfIntegers Class
TestStackOfIntegers
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