Java OOP Interview Questions

OOP encapsulates data and behavior using inheritance, polymorphism, encapsulation, and abstraction to build maintainable, reusable code.

class Animal {
  void sound() {
  }
}
class Dog extends Animal {
  @Override void sound() {
    System.out.println("Bark");
  }
}
Dog dog = new Dog();
dog.sound();

Encapsulation (data hiding), Abstraction (hide complexity), Inheritance (code reuse), Polymorphism (runtime behavior determination).

class Animal {
  void sound() {
  }
}
class Dog extends Animal {
  void sound() {
    System.out.println("Bark");
  }
}
interface Pet {
  void play();
}
class Cat implements Pet {
  public void play() {
    System.out.println("Play");
  }
}

Polymorphism is the ability of objects to take multiple forms,method overloading (compile-time) and method overriding (runtime) enable subclasses to override parent behavior.

class Animal {
  void sound() {
  }
}
class Dog extends Animal {
  void sound() {
    System.out.println("Woof");
  }
}
Animal a = new Dog();
a.sound();

OOP provides modularity, reusability, and encapsulation; procedural is simpler but lacks abstraction; functional emphasizes immutability and composition,OOP balances power and complexity.

OOP provides modularity, reusability, and encapsulation; procedural is simpler but less maintainable; functional enables parallelization and immutability but has steeper learning curve.

Inheritance allows a class to acquire properties and methods from a parent class, enabling code reuse and establishing an 'is-a' relationship in OOP hierarchy.

Abstraction hides implementation complexity and exposes only essential features through interfaces or abstract classes, simplifying usage for clients.

Messaging is communication between objects where one object sends a message (method call) to another to request an action.

An interface is a contract defining abstract methods that implementing classes must provide; enables polymorphism and multiple inheritance of type.

'is-a' implies inheritance (class extends parent), while 'has-a' implies composition (object contains another object as a member).

Composition is strong ownership where the parent controls the child's lifecycle; aggregation is weak association where objects are independent.