Object-Oriented Concepts

Object-oriented programming (OOP) organizes software design around objects rather than actions. In Java, this approach models real-world entities with properties (attributes) and behaviors (methods).

Key Differences from Procedural Programming

• Procedural: Focuses on step-by-step execution
• Object-oriented: Emphasizes objects and their interactions

Example: Washing clothes

• Procedural: Detailed manual steps
• OOP: Using a washing machine object

Core OOP Features

1. Encapsulation
2. Inheritance
3. Polymorphism

Classes and Objects

A class defines a blueprint for objects, specifying their attributes and methods. An object is a specific instance of a class.

Example class definition:

public class Animal {
    // Attributes
    String name;
    int age;
    
    // Behaviors
    public void eat() {
        System.out.println("Eating...");
    }
    
    public void sleep() {
        System.out.println("Sleeping...");
    }
}

Creating and Using Objects

public class Main {
    public static void main(String[] args) {
        Animal cat = new Animal();
        cat.name = "Whiskers";
        cat.age = 3;
        
        cat.eat();
        cat.sleep();
    }
}

Memory Management

• Objects reside in heap memory
• References to objects live in stack memory
• Methods are stored once in class definition

Encapsulation

Encapsulation protects data by restricting direct access to class members. Use private variables with public getter/setter methods.

Example:

public class BankAccount {
    private double balance;
    
    public void setBalance(double amount) {
        if (amount > 0) {
            this.balance = amount;
        }
    }
    
    public double getBalance() {
        return balance;
    }
}

Constructors

Constructors initialize new objects. Java provides a default no-arg constructor if none is defined.

public class Book {
    private String title;
    private String author;
    
    // Default constructor
    public Book() {}
    
    // Parameterized constructor
    public Book(String title, String author) {
        this.title = title;
        this.author = author;
    }
}

JavaBean Standard

A proper JavaBean includes:

1. Private feilds
2. Public no-arg constructor
3. Getter/setter methods
4. Serializable implmeentation (optional)

Example:

public class Employee implements Serializable {
    private String id;
    private String department;
    
    public Employee() {}
    
    public Employee(String id, String dept) {
        this.id = id;
        this.department = dept;
    }
    
    // Getters and setters
    public String getId() {
        return id;
    }
    
    public void setId(String id) {
        this.id = id;
    }
    
    // Additional methods...
}