If you're getting ready for your first interview for an Object-Oriented Programming (OOPs) role, congratulations! We know you've put in a lot of time and effort to get this far. You're probably now wondering what kinds of OOPs interview questions to expect.
That's why we've put together this list of 13 common OOPs interview questions and how to answer them. Between studying these OOPs-specific questions and our guide on technical interviews, you'll feel confident and prepared before the big day.
1. What are OOPs?
Object-oriented programming is a programming model based on objects rather than procedures or functions. Objects contain data as well as methods, or functions, that operate on that data.
2. What are the advantages of OOPs?
There are many advantages to OOPs, including:
- OOPs abstraction helps make code easier to use and understand.
- OOPs reuse code which helps reduce redundancy and save coding time.
- OOPs can easily handle and manipulate complex datasets.
- OOPs support a lot of flexibility through polymorphism.
3. What are some examples of OOP languages?
The most popular OOP languages are:
4. What are the four main concepts of OOPs?
The four main concepts or principles of OOPs are:
5. What is encapsulation?
Encapsulation refers to the consolidation or bundling of all data and methods into a single unit. At the same time, encapsulation hides or restricts any unnecessary data and methods to minimize complexity.
For example, if you define an object that contains a list of integers, your object will always include the method used to calculate the average of those integers, even if you can't access the source code directly.
6. What is polymorphism?
Polymorphism is the concept of having a single function or method do different things depending on the object class. For example, using the "+" operator will perform a summation if the inputs are numbers. But the same "+" operator will perform concatenation if the inputs are strings. In other words, the "+" is an operator that takes on several forms — it's polymorphic.
7. What is inheritance?
Inheritance is the concept of a class or object gaining certain properties and methods from a parent class.
For example, suppose we created an "Animals" class with properties like age and weight. If we create a child class called "Mammals," we might add mammal-specific traits like hair color. But, as a child class of "Animals," the "Mammals" class would automatically inherit properties of age and weight. That's how inheritance works in OOPs.
8. What is abstraction?
Abstraction is the concept of hiding unnecessary details about an object, method, or function from someone using your program. For example, when you use a coffeemaker to brew a cup of coffee in the morning, all you need to do is add water and coffee beans. You don't need to understand the mechanics of your coffeemakers or how the sensors are calibrated.
So, while your code may include a complex function or method, following abstraction means that anyone using your program only needs to provide the necessary inputs for the function or method to work. And the only outputs are those that are useful to the person using your program.
9. What's the difference between a class and an object?
In other words, all objects belong to a class that defines the object's properties and how that object can interact with other objects. And, while you need to declare a class only once, you can create as many objects as you need to — even objects that are part of the same class.
10. What are subclasses and superclasses?
A subclass is a class that inherits from another class. For example, you can create a class called "Animals" that includes properties such as age, weight, and natural habitat. These properties can apply to any animal.
When you create a subclass called "Birds," the subclass, or child class, inherits everything from the parent "Animals" class — age, weight, and natural habitat — but can also include bird-specific attributes like egg size and wingspan.
A superclass is a class that acts as a parent to one or more child classes or subclasses.
11. What is method overloading?
Method overloading is creating different methods that are defined under different classes but share the same name. For example, if you have two classes, "Dogs" and "Cats," then you may assign both classes a method with the same name, "Speak."
For "Dogs," the "Speak" method outputs "Woof," while for "Cats," the method outputs "Meow." When you create a new object, "MyPet," and call the "Speak" method, the output will be different, depending on whether "MyPet" falls within the "Dogs" or "Cats" class.
12. What is a constructor?
A constructor is a special method or subroutine of a class that initializes a new object of that class. When the object is first declared or created, the constructor sets values to properties of the object, which can be default values or user-defined. Constructors will have the same names as the class itself, but they're not considered to be true methods because they don't have a return type.
13. What is an exception?
An exception is a problem that interrupts program execution. For example, an exception may occur when a user inputs a string into a function that only accepts integers. Proper exception handling can resolve many exceptions — for example, checking that input data is the correct type and displaying a notification that the function only accepts integers.
Be prepared for your next OOPs interview
We know you have what it takes to succeed as an OOPs developer. Once you've mastered these OOPs interview questions, make sure to check out our guide to technical interviews as well as our technical portfolio guide to make sure you're ready for anything. A little interview prep goes a long way toward impressing the hiring manager!
Then, once you're ready to start practicing with real technical interview questions, test your coding skills with one of our Code Challenges. Not only will they give you a sense of what to expect when you walk into your first technical interview, but they'll also help you identify the concepts you'll need to refresh your knowledge of if you find yourself stuck.
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