Unit 7: Object-Oriented Programming

Classes and Objects

• Definition: A class is a blueprint for creating objects. It defines attributes (fields) and methods (functions) that objects of the class will have.
• Example:

  class Car {
      String make;
      String model;
      int year;
  
      void startEngine() {
          // Code to start the car's engine
      }
  }
  

Constructors

• Definition: Constructors are special methods used to initialize objects when they are created. They have the same name as the class and no return type.
• Example:

  class Car {
      String make;
      String model;
      int year;
  
      Car(String make, String model, int year) {
          this.make = make;
          this.model = model;
          this.year = year;
      }
  }
  

Inheritance

• Definition: Inheritance allows a subclass to inherit attributes and methods from a superclass. It promotes code reuse and supports the “is-a” relationship.
• Example:

  class Animal {
      String name;
        
      void eat() {
          // Code for eating
      }
  }
  
  class Dog extends Animal {
      void bark() {
          // Code for barking
      }
  }
  

Polymorphism

• Definition: Polymorphism allows objects of different classes to be treated as objects of a common superclass. It supports method overriding and dynamic binding.
• Example:

  class Animal {
      void makeSound() {
          // Default animal sound
      }
  }
  
  class Dog extends Animal {
      @Override
      void makeSound() {
          // Dog's sound
      }
  }
  

Encapsulation

• Definition: Encapsulation restricts access to certain components of an object and hides the internal details. It uses private and public access modifiers.
• Example:

  class Student {
      private int age;
        
      public int getAge() {
          return age;
      }
        
      public void setAge(int age) {
          if (age >= 0) {
              this.age = age;
          }
      }
  }
  

Abstraction

• Definition: Abstraction focuses on the essential features of an object while hiding unnecessary details. It uses abstract classes and methods.
• Example:

  abstract class Shape {
      abstract double area();
  }
  
  class Circle extends Shape {
      double radius;
        
      @Override
      double area() {
          return Math.PI * radius * radius;
      }
  }
  

Static Members

• Definition: Static members (variables and methods) belong to the class itself rather than instances of the class. They are accessed using the class name.
• Example:

  class MathUtils {
      static final double PI = 3.14159265359;
        
      static int add(int a, int b) {
          return a + b;
      }
  }