Object-Oriented Programming in Java
Object-Oriented Programming (OOP) is a programming paradigm based on the concept of objects, which can contain data (fields) and methods (functions). Java is a fully object-oriented language (except for primitive types), and understanding its OOP principles is essential for effective Java development.
🔑 Core Principles of OOP in Java
Encapsulation
Inheritance
Polymorphism
Abstraction
1. 🛡️ Encapsulation
Encapsulation means hiding internal details of a class and exposing only what is necessary through public methods (getters/setters).
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public class Person {
private String name; // private = encapsulated
private int age;
public String getName() {
return name;
}
public void setName(String newName) {
name = newName;
}
}
2. 🧬 Inheritance
Inheritance allows one class (subclass) to inherit fields and methods from another class (superclass), promoting code reuse.
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class Animal {
void speak() {
System.out.println("Animal speaks");
}
}
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
3. 🎭 Polymorphism
Polymorphism means "many forms". In Java, this allows you to call the same method on different objects and get different results.
Compile-time Polymorphism (Method Overloading):
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class MathUtil {
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
}
Runtime Polymorphism (Method Overriding):
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class Animal {
void makeSound() {
System.out.println("Animal sound");
}
}
class Cat extends Animal {
@Override
void makeSound() {
System.out.println("Meow");
}
}
4. 🧩 Abstraction
Abstraction means hiding complex implementation details and showing only essential features.
Abstract Class Example:
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abstract class Vehicle {
abstract void drive(); // abstract method
}
class Car extends Vehicle {
void drive() {
System.out.println("Driving a car");
}
}
Interface Example:
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interface Flyable {
void fly();
}
class Bird implements Flyable {
public void fly() {
System.out.println("Bird is flying");
}
}
🎯 Why Use OOP in Java?
Modularity: Code is organized into classes.
Reusability: Inheritance allows you to reuse existing code.
Scalability: Easy to manage and scale large applications.
Security: Encapsulation protects data and logic.
🛠 Real-World Example
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class BankAccount {
private double balance;
public void deposit(double amount) {
if (amount > 0)
balance += amount;
}
public void withdraw(double amount) {
if (amount <= balance)
balance -= amount;
}
public double getBalance() {
return balance;
}
}
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