Abstract Class Interview Questions

What is abstract class?

What is a good example of abstract class?

A good example of an abstract class is a “Shape” class in a drawing application. It may have abstract methods like “calculateArea()” and “calculatePerimeter()” that represent common behavior for all shapes, but it cannot be instantiated itself since there is no specific “Shape” in the real world. Subclasses like “Circle,” “Rectangle,” and “Triangle” can be derived from the abstract class, providing their own implementations for the abstract methods to represent their unique properties and behavior.

What is the main purpose of abstract class?

The main purpose of an abstract class is to provide a blueprint for other classes to inherit from and enforce the implementation of certain methods. It allows the definition of common behavior and attributes while ensuring that subclasses provide specific implementations for abstract methods, promoting code reusability and enforcing a consistent structure among related classes.

How to achieve abstraction in Java interview questions?

1. Abstract Classes: Explain what abstract classes are, how to declare them using the “abstract” keyword, and how they can have both abstract (without implementation) and concrete methods.

2. Interfaces: Describe interfaces as a way to achieve full abstraction, allowing classes to implement multiple interfaces, and how they define a contract that implementing classes must adhere to.

3. Differences between Abstract Classes and Interfaces: Highlight the distinctions between abstract classes and interfaces, such as multiple inheritance for interfaces and single inheritance for abstract classes.

4. Use Cases: Discuss situations where abstraction is beneficial, such as designing frameworks or APIs where you want to define common behavior without worrying about the specific implementations.

5. Real-World Examples: Provide examples from standard Java libraries where abstraction is used, like the “Collections” framework, where interfaces define common behaviors for different data structures.

Which is called abstract class?

A class that contains one or more abstract methods and is declared with the “abstract” keyword is called an abstract class.

Can you explain abstract class?

An abstract class is a class in Java that cannot be instantiated on its own. It serves as a blueprint for other classes to inherit from. It may contain both abstract methods (methods without implementation) and concrete methods (methods with implementation). Subclasses derived from the abstract class must provide implementations for the abstract methods, making it a way to define common behavior while enforcing specific implementations in child classes.

What is a real life example of abstract?

A real-life example of abstraction can be seen in a “Vehicle” class. In this case, the “Vehicle” class can be an abstract class that defines common attributes and behaviors for all vehicles, such as “startEngine(),” “stopEngine(),” and “accelerate().” Concrete subclasses like “Car,” “Motorcycle,” and “Truck” can inherit from the “Vehicle” abstract class and provide specific implementations for these common methods to represent their distinct functionalities.

What are 5 examples of abstract data types?

Abstract Data Types (ADTs) are data structures that provide an abstract representation of data and define operations to manipulate that data without specifying the underlying implementation. Here are five examples of abstract data types:

1. Stack: A data structure that follows the Last-In-First-Out (LIFO) principle, where elements are added and removed from the same end (the top). Common operations include push (add), pop (remove), and peek (view the top element).
2. Queue: A data structure that follows the First-In-First-Out (FIFO) principle, where elements are added at the rear and removed from the front. Common operations include enqueue (add), dequeue (remove), and peek (view the front element).
3. Linked List: A collection of elements where each element points to the next one, forming a chain. Linked lists can be singly linked (one-way) or doubly linked (two-way). Common operations include insertion, deletion, and traversal.
4. Hash Table: A data structure that stores key-value pairs, allowing efficient retrieval of values based on their keys. It uses a hashing function to map keys to indices in an array, reducing search time.
5. Binary Search Tree: A binary tree where each node has at most two children, and the left child is smaller than the parent, while the right child is larger. It allows fast searching, insertion, and deletion of elements, making it suitable for many applications like searching and sorting.

What is advantage of abstract class?

The advantage of an abstract class is that it allows you to define common behavior and attributes once and have multiple subclasses inherit from it, promoting code reusability and maintaining a consistent structure across related classes. Abstract classes also enforce the implementation of specific methods in subclasses, ensuring that the necessary behavior is provided in each derived class.

Can an abstract class have a constructor?

Yes, an abstract class can have a constructor. However, the purpose of an abstract class is to serve as a blueprint for its subclasses, and it cannot be instantiated on its own. Therefore, the constructor of an abstract class is typically used to initialize the common state or behavior shared by its subclasses when they are instantiated. Subclasses must call the constructor of the abstract class using the super() keyword in their own constructors to ensure proper initialization of the shared attributes.

Why do we need abstract?

We need abstraction to simplify complex systems by hiding unnecessary details and exposing only relevant functionalities. Abstraction allows us to create models, such as abstract classes and interfaces in Java, that define a common structure and behavior for related objects. This promotes code reusability, modular design, and better maintenance. By using abstraction, developers can focus on high-level concepts and interactions, making code more manageable and understandable.

Can we achieve 100% abstraction in Java?

Yes, we can achieve 100% abstraction in Java by using interfaces, which allow us to define fully abstract classes with all methods declared but not implemented.

Why abstract methods Cannot be static?

Abstract methods cannot be static because they require an instance of the class to be overridden by the subclass. Static methods belong to the class itself and are not tied to any specific instance, so they cannot be overridden by subclasses. Abstract methods, on the other hand, must be implemented in concrete subclasses, and their behavior may vary depending on the instance of the subclass.

How to remove abstraction in Java?

To remove abstraction in Java, you need to provide concrete implementations for all the abstract methods in an abstract class or interface. This means removing the “abstract” keyword from the class declaration and implementing the previously abstract methods with actual code. By doing so, you eliminate the abstraction layer and create a fully functional class with all its methods defined and implemented.

Is abstract class a data type?

No, an abstract class is not a data type. It is a special type of class in object-oriented programming used to define a blueprint for other classes. Abstract classes cannot be instantiated on their own; they serve as a base for other classes to inherit from and provide a way to define common behavior and enforce specific implementations in subclasses.