Object Oriented Programming

1. What are object oriented concepts? What is difference between object-based, object-oriented and fully object-oriented language?

   Object-oriented concepts include encapsulation, abstraction, inheritance, and polymorphism.

   Object-based languages support objects but lack inheritance and polymorphism (e.g., JavaScript pre-ES6).

   Object-oriented languages support objects, classes, and inheritance (e.g., C++, early Java).

   Fully object-oriented languages treat everything as objects, including primitive types (e.g., Smalltalk, Ruby).

2. What are advantages of Object-Oriented Programming? What is data security?

   Advantages of OOP:

   • Modularity and reusability
   • Easier maintenance
   • Better organization through classes
   • Natural problem modeling
   • Scalability

   Data security in OOP refers to protecting data through encapsulation by making fields private and only accessible through controlled methods.

3. What is class and object? Give real-life example.

   A class is a blueprint/template that defines properties and behaviors.

   An object is an instance of a class with specific values for its properties.

   Real-life example: Car (class) vs. a specific Toyota Camry with VIN 1234 (object).

4. What are characteristics of object? Explain them.

   • Identity: Unique identification
   • State: Data stored in fields/attributes
   • Behavior: Methods defining operations
   • Encapsulation: Hiding internal details
   • Inheritance: Ability to inherit properties/methods from parent

5. What is the need of getter and setter functions in class?

   Getters and setters:

   • Control access to private fields
   • Allow validation before changing values
   • Enable read-only or write-only properties
   • Provide abstraction from internal representation
   • Can trigger additional actions when values change

6. What is abstraction and encapsulation. Give real-life example.

   Abstraction: Exposing essential features while hiding complexity. Example: Car dashboard (exposes speed, fuel without engine complexity)

   Encapsulation: Bundling data and methods, restricting direct access to data. Example: Medicine capsule (contents packaged and accessed only by intended means)

7. What is polymorphism? What are its types? Explain them with examples.

   Polymorphism: Ability of objects to take multiple forms.

   Types:

   • Compile-time/Static: Method overloading, operator overloading Example: add(int, int) and add(double, double)
   • Runtime/Dynamic: Method overriding Example: Animal.makeSound() overridden by Dog.makeSound()

8. What is method overloading? Which are the rules of method overloading? Why return type is not considered in method overloading?

   Method overloading: Multiple methods with same name but different parameters.

   Rules:

   • Must have different parameter types, count, or order
   • Cannot differ by only return type
   • Cannot differ by only access modifiers

   Return type isn't considered because the compiler identifies methods by signature (name and parameters) during method calling. Return types alone don't provide enough information at the call site.

9. What are different types of hierarchy? When to use which one?

   • Single inheritance: One parent (use for "is-a" relationships)
   • Multiple inheritance: Multiple parents (often avoided due to complexity)
   • Multilevel inheritance: Chain of inheritance (use for specialization chains)
   • Hierarchical inheritance: One parent, multiple children (common classifications)
   • Hybrid inheritance: Combination of types (use for complex relationships)

10. What is the difference between method overloading and method overriding?

    Overloading:

    • Same method name, different parameters
    • Happens in same class
    • Compile-time polymorphism
    • Enhances readability

    Overriding:

    • Same method name and parameters
    • Happens in parent-child classes
    • Runtime polymorphism
    • Implements specialized behavior

11. What is object slicing? Explain object slicing in context of up-casting?

    Object slicing occurs when a derived class object is assigned to a base class object, causing loss of derived class-specific members.

    In upcasting, a derived class reference is converted to a base class reference. If done through object assignment rather than reference, slicing occurs.

12. What is down-casting and when it is required? Explain with code.

    Downcasting is casting a base class reference to a derived class reference.

    Required when:

    • Accessing derived class-specific members through a base class reference

    Animal animal = new Dog(); // Upcasting
    // animal.bark(); // Error - Animal doesn't have bark()
    
    Dog dog = (Dog)animal; // Downcasting
    dog.bark(); // Now works
    
    

13. What do you know about association, composition and aggregation? Explain with the help of example.

    Association: Relationship between objects Example: Teacher and Student (have relationship but independent lifecycle)

    Aggregation: "has-a" relationship, weak ownership Example: Department and Professors (department has professors, but they exist independently)

    Composition: "part-of" relationship, strong ownership Example: House and Rooms (rooms cannot exist without house)

14. What are different types of inheritance? Explain with the help of example. What are problems with multiple inheritance?

    Types:

    • Single: Class B extends Class A
    • Multiple: Class C extends Class A, B (Java doesn't support)
    • Multilevel: Class C extends B extends A
    • Hierarchical: Class B, C both extend A
    • Hybrid: Combination of above

    Problems with multiple inheritance:

    • Diamond problem (ambiguity when same method exists in multiple parents)
    • Complexity in managing hierarchies
    • Potential conflicts between inherited members

15. What is difference between interface, abstract class and non-abstract class? Which one to use where?

    Interface:

    • Only method declarations (Java 8+ allows defaults)
    • Supports multiple inheritance
    • Use when defining a contract without implementation

    Abstract class:

    • Can have concrete and abstract methods
    • Can have constructor, fields
    • Single inheritance only
    • Use for partial implementation and common base functionality

    Non-abstract class:

    • All methods implemented
    • Can be instantiated
    • Use for concrete implementations

16. Which are the different types of design pattern? Explain singleton design pattern.

Java Programming

1. What is a collection framework? Explain any 2 classes in Java Collections.
2. What is functional programming? Explain stream programming with examples.