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Object-Oriented Design for a Library App

Model books, borrowers, and loans using classes, responsibilities, and simple object collaboration.

Intermediate 75 minutes John IT 111 ยท Computer Programming 1 Created Aug 31, 2026 5:55 AM

Explanation

Object-oriented design represents a system through objects that combine data and behavior. Good class design begins with responsibilities rather than creating a class for every noun.

Students model a small library application, identify useful relationships, and implement borrowing rules. They then discuss encapsulation and how clear interfaces reduce accidental misuse.

Learning activities

  1. Identify candidate objects and their responsibilities.
  2. Draw a simple class relationship diagram.
  3. Implement and test one borrowing rule.

Code example

python
class Book:
    def __init__(self, title):
        self.title = title
        self.is_available = True

    def borrow(self):
        if not self.is_available:
            return False
        self.is_available = False
        return True

Knowledge check

1. What should guide the creation of a class?

  • Its responsibility
  • The length of its name
  • The screen color
Show answer

Its responsibility

References