Section 0:

Java Package creation Guide

Part 1

1. First, create a directory called lab4. After that, when writing the Java classes, define the package name (lab4) to match the directory structure.

Mainclass.java

HelperClass.java

When compiling and running the program, please follow the commands below. Make sure to navigate outside the created folder (lab4) before compiling the program.

Part 2

If there has many packages like below

Mainclass.java

HelperClass.java

When compiling and running the program, please follow the commands below. Make sure to navigate outside the created folder before compiling the program.

Section 1: Notes

Basics of Classes

• A class is a blueprint for creating objects.
• A class defines attributes (fields/variables) and methods (functions) that describe the behavior of the objects created from the class.
• Example:

  public class Car {
      // Attributes
      String color;
      String model;
      int year;
      
      // Methods
      void drive() {
          System.out.println("The car is driving");
      }
  }

Visibility Levels

• public: Accessible from any other class.
• private: Accessible only within the same class.
• protected: Accessible within the same package and subclasses.
• default (no modifier): Accessible only within the same package.

    java
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    public class Car {
        public String color;
        private String model;
        protected int year;
        int speed; // default
    }

Attributes

• Variables that hold the data associated with an object.
• Declared within a class but outside any method.

    java
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    public class Car {
        String color; // attribute
        String model; // attribute
    }

Operations (Methods)

• Functions that define the behavior of objects.
• Can be used to perform operations, return values, or modify object state.

java
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public class Car {
    void drive() {
        System.out.println("The car is driving");
    }
}

Creating Objects and Accessing Variables

• Objects are instances of classes.

• Use the new keyword to create an object.

• Access attributes and methods using the dot . operator.

    java
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    public class Car {
        String color;
        String model;
        
        void drive() {
            System.out.println("The car is driving");
        }
        
        public static void main(String[] args) {
            Car myCar = new Car(); 
            myCar.color = "Red";
            myCar.model = "Toyota";
            System.out.println(myCar.color); // Outputs: Red
            myCar.drive(); // Outputs: The car is driving
        }
    }
  

# Getters and Setters

- Methods that provide access to private attributes.
- Getters return the value of a private attribute.
- Setters allow modifying the value of a private attribute.
   

java
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public class Car {
    private String color;
    private String model;
    
    // Getter for color
    public String getColor() {
        return color;
    }
    
    // Setter for color
    public void setColor(String color) {
        this.color = color;
    }
    
    // Getter for model
    public String getModel() {
        return model;
    }
    
    // Setter for model
    public void setModel(String model) {
        this.model = model;
    }
}

`` `

Section 2: Basic Guided Questions

1. Creating a Class and Objects:

   • Write a class Dog with attributes name and breed.
   • Write a method bark() that prints "Woof!".
   • Create an object of the class and call the bark() method.

2. Using Visibility Levels:

   • Modify the Dog class to have name as public and breed as private.
   • Add a method getBreed() to return the breed.
   • Try accessing breed directly from another class and observe the result.
   • Explanation Required: Explain why breed cannot be accessed directly and how the getBreed() method allows access.
   • Create a class Person with the following attributes and methods:
     • private String name
     • protected int age
     • public String getName()
     • public void setName(String name)
     • protected void setAge(int age)
   • Try accessing the attributes and methods of the Person class from another class in the same package and from a different package.
   • Explanation Required: Explain the access levels for each visibility modifier when accessing the Person class attributes and methods.

3. Visibility Check for Classes and Methods in Packages:

   • Create a package mypackage and a class Person inside it.
   • Create another class TestPerson in the same package and try accessing the Person class.
   • Create another package anotherpackage and a class TestPersonInAnotherPackage inside it. Try accessing the Person class from this new class.
   • Explanation Required: Explain the class access levels within and across packages.

4. Using Getters and Setters:

   • Modify the Book class to make the attributes title and author private.
   • Add getters and setters for these attributes.
   • Try accessing the private attributes directly and explain the result.
   • Explanation Required: Explain the purpose of getters and setters and how they provide controlled access to private attributes.

Section 3: Comprehensive Question

Software Requirement Specification for a Library Management System:

The Library Management System (LMS) shall manage books and member details, including borrowing and returning books. The system shall consist of the following requirements:

1. Book Management:

   • The system shall allow adding new books with the following details: title, author, ISBN, and availability status.
   • The system shall allow searching for books by title.
   • The system shall allow updating the availability status of a book when it is borrowed or returned.

2. Member Management:

   • The system shall allow registering new members with their details: name and member ID.
   • The system shall allow searching for members by their member ID.
   • The system shall track books borrowed by each member.

3. Borrowing and Returning Books:

   • The system shall allow members to borrow available books.
   • The system shall update the book's availability status when borrowed.
   • The system shall allow members to return borrowed books.
   • The system shall update the book's availability status when returned.

4. Example Implementation:

Requirement: The system shall allow searching for books by title.

Implementation Steps:

• Store the list of books in an array.
• Loop through the array and compare each book's title with the search query.
• If a match is found, return the book details. Code Example:

java
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public class Library {
    private Book[] books;
    private int bookCount;

    public Library(int size) {
        books = new Book[size];
        bookCount = 0;
    }

    public void addBook(Book book) {
        if (bookCount < books.length) {
            books[bookCount] = book;
            bookCount++;
        }
    }

    public Book searchBookByTitle(String title) {
        for (int i = 0; i < bookCount; i++) {
            if (books[i].getTitle().equalsIgnoreCase(title)) {
                return books[i];
            }
        }
        return null;
    }
}