OOP Basics
Object-Oriented Programming (OOP) is a paradigm that organizes code into objects containing data and behavior. Java is an OOP language, and understanding OOP helps structure complex DSA code.
Class and Object
A class is a blueprint; an object is an instance.
public class Student {
// fields (data)
String name;
int age;
// constructor
Student(String name, int age) {
this.name = name;
this.age = age;
}
// method
void display() {
System.out.println(name + ", " + age);
}
}
// Creating object
Student s = new Student("Alice", 20);
s.display();
Four Pillars of OOP
- Encapsulation – Hide data using private fields and public getters/setters.
- Inheritance – A class can inherit from another (extends).
- Polymorphism – Same method can have different implementations (overriding).
- Abstraction – Hide complexity using abstract classes/interfaces.
Example of Inheritance
public class Animal { void sound() { System.out.println("Animal sound"); } }
public class Dog extends Animal { void sound() { System.out.println("Bark"); } }
Two Minute Drill
- Class = blueprint; Object = instance.
- Constructor initializes objects.
- Encapsulation: data hiding with private + public methods.
- Inheritance: code reuse with extends.
- Polymorphism: method overriding/runtime behavior.
- Abstraction: using abstract classes/interfaces.
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