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Classes and Objects Exercises

This directory contains exercises to help you practice creating and working with classes and objects in Java using jshell.

Setup

  1. Open your terminal/command prompt
  2. Navigate to this directory
  3. Start jshell: jshell
  4. Load the exercise file: /open topic.jsh

Exercises

Exercise 1: Basic Class Creation

Create a class Person with two fields: String name and int age. Write a constructor that takes name and age as parameters. Add a method introduce() that returns a String like "Hello, I'm John and I'm 25 years old."

Exercise 2: Class with Methods

Create a class BankAccount with fields: String accountNumber and double balance. Add a constructor that sets the account number and starts with a balance of 0.0. Add methods:

  • deposit(double amount) - adds money to the balance
  • withdraw(double amount) - removes money (if sufficient funds exist)
  • getBalance() - returns current balance
  • getAccountInfo() - returns account details as a string

Exercise 3: Object Creation and Usage

Write methods that demonstrate object creation:

  • createPerson(String name, int age) - creates and returns a Person object
  • createBankAccount(String accountNumber) - creates and returns a BankAccount object
  • demonstratePersonUsage() - creates a Person, calls introduce(), and prints the result

Exercise 4: Working with Multiple Objects

Create a class Car with fields: String brand, String model, and int year. Add appropriate constructor and methods:

  • getCarInfo() - returns formatted car information
  • isClassic() - returns true if car is more than 25 years old Write a method compareCars(Car car1, Car car2) that compares two cars and returns which is older.

Exercise 5: Object State and Behavior

Create a class Counter with:

  • int count field (starts at 0)
  • increment() method - increases count by 1
  • decrement() method - decreases count by 1
  • reset() method - sets count back to 0
  • getCount() method - returns current count value

Exercise 6: Class with Validation

Create a class Student with fields: String name, int grade, and double gpa. Add constructor with validation:

  • Name cannot be null or empty
  • Grade must be between 1 and 12
  • GPA must be between 0.0 and 4.0 Add methods:
  • isHonorStudent() - returns true if GPA >= 3.5
  • getStudentInfo() - returns formatted student information

Exercise 7: Object Interaction

Create a class Book with: String title, String author, and boolean isCheckedOut. Create a class Library with an ArrayList to store books. Add methods to Library:

  • addBook(Book book) - adds a book to the collection
  • checkOutBook(String title) - marks book as checked out if available
  • returnBook(String title) - marks book as available
  • getAvailableBooks() - returns count of available books

Testing Your Code

After completing each exercise, test your classes and methods:

// Example tests
Person Person = createPerson("Alice", 30);
    return (person.introduce());

BankAccount account = createBankAccount("123456");
account.deposit(100.0);
account.withdraw(30.0);
System.out.println("Balance: " + account.getBalance()); // Should be 70.0

Car car1 = new Car("Toyota", "Camry", 1995);
Car car2 = new Car("Honda", "Civic", 2020);
System.out.println(car1.isClassic()); // Should be true

Counter counter = new Counter();
counter.increment();
counter.increment();
System.out.println(counter.getCount()); // Should be 2

Tips

  • Read the NOTES.md file first to understand classes and objects
  • Remember that classes are blueprints, objects are instances
  • Use meaningful names for classes (PascalCase) and methods (camelCase)
  • Always validate input in constructors and methods
  • Test your objects by creating instances and calling methods
  • Think about what data (fields) and behavior (methods) each class should have