Top 50 OOP Interview Questions and Answers

OOP Interview Questions and Answers

see below for a list of OOP interview questions with answers

What Is Object-Oriented Programming?

Object-Oriented Programming (OOP) is a programming paradigm where the complete software operates as a bunch of objects talking to each other. An object is a collection of data and methods that operate on its data.

Why OOP?

The main advantage of OOP is better manageable code that covers the following.

1) The overall understanding of the software is increased as the distance between the language spoken by developers and that spoken by users.

2) Object orientation eases maintenance by the use of encapsulation. One can easily change the underlying representation by keeping the methods the same.

OOP paradigm is mainly useful for relatively big software. See this for a complete example that shows the advantages of OOP over procedural programming.

What are the various elements of OOP?

Various elements of OOP are:

– Object
– Class
– Method
– Encapsulation
– Information Hiding
– Inheritance
– Polymorphism

What is Abstraction?

Abstraction is an OOPS concept to construct the structure of real-world objects. During this construction, only the general states and behaviors are taken and more specific states and behaviors are left aside for the implementers.

What is Encapsulation?

Encapsulation is an OOPS concept to create and define the permissions and restrictions of an object and its member variables and methods. A very simple example to explain the concept is to make the member variables of a class private and provide public getter and setter methods. Java provides four types of access level modifiers: public, protected, no modifier, and private.

What is the difference between Abstraction and Encapsulation?

“Program to interfaces, not implementations” is the principle for Abstraction, and “Encapsulate what varies” is the OO principle for Encapsulation.
Abstraction provides a general structure of a class and leaves the details for the implementers. Encapsulation is to create and define the permissions and restrictions of an object and its member variables and methods.
Abstraction is implemented in Java using the interface and abstract class while Encapsulation is implemented using four types of access level modifiers: public, protected, no modifier, and private.

What is Polymorphism?

Polymorphism is the occurrence of something in various forms. Java supports various forms of polymorphism like polymorphic reference variables, polymorphic methods, polymorphic return types, and polymorphic argument types.
What is Inheritance?

A subclass that can inherit the states and behaviors of its superclass is known as inheritance.

What is multiple Inheritance?

A child class inheriting states and behaviors from multiple parent classes is known as multiple Inheritance.
What is the diamond problem in inheritance?

In the case of multiple Inheritance, suppose class A has two subclasses B and C, and class D has two superclasses B and C.If a method present in A is overridden by both B and C but not by D then from which class D will inherit that method B or C? This problem is known as a diamond problem.

Why Java does not support multiple Inheritance?

Java was designed to be a simple language and multiple Inheritance introduces complexities like a diamond problem. Inheriting states or behaviors from two different types of classes is a case that in reality very rare and it can be achieved easily through an object association.

What are Static Binding and Dynamic Binding?

Static or early binding is resolved at compile time. Method overloading is an example of static binding.

Dynamic or late or virtual binding is resolved at run time. Method overriding is an example of dynamic binding.

What is the meaning of the “IS-A” and “HAS-A” relationship?

“IS-A” relationship implies inheritance. A sub-class object is said to have an “IS-A” relationship with the superclass or interface. If class A extends B then A “IS-A” B. It is transitive, that is, if class A extends B and class B extends C then A “IS-A” C. The “instanceof” operator in java determines the “IS-A” relationship.

When class A has a member reference variable of type B then A “HAS-A” B. It is also known as Aggregation.

What is Association?

Association is a relationship between two objects with multiplicity.

What is Aggregation?

Aggregation is also known as the “HAS-A” relationship. When class Car has a member reference variable of type Wheel then the relationship between the classes Car and Wheel is known as Aggregation. Aggregation can be understood as a “whole to its parts” relationship.

The car is the whole and the Wheel is part. The wheel can exist without the Car. Aggregation is a weak association.

What is Composition?

A composition is a special form of Aggregation where the part cannot exist without the whole. Composition is a strong Association. The composition relationship is represented as aggregation with one difference that the diamond shape is filled.

What is Dependency?

When one class depends on another because it uses that at some point in time then this relationship is known as Dependency. One class depends on another if the independent class is a parameter variable or local variable of a method of the dependent class. A Dependency is drawn as a dotted line from the dependent class to the independent class with an open arrowhead pointing to the independent class.

What is the difference between Association and Dependency?

The main difference between Association and Dependency is in the case of Association one class has an attribute or member variable of the other class type but in the case of Dependency a method takes an argument of the other class type or a method has a local variable of the other class type.

What is a Class?

A class is the specification or template of an object.

What is an Object?

The object is an instance of the class.

What are the advantages of OOPS concepts?

Major advantages of OOPS programming are;

Simplicity: OOPS programming objects model real-world objects, so the complexity is reduced and the program structure is clear.
Modularity: Each object forms a separate entity whose internal workings are decoupled from other parts of the system.
Modifiability: It is easy to make minor changes in the data representation or the procedures in an OO program. Changes inside a class do not affect any other part of a program, since the only public interface that the external world has to a class is through the use of methods.
Extensibility: adding new features or responding to changing operating environments can be solved by introducing a few new objects and modifying some existing ones.
Maintainability: Objects can be maintained separately, making locating and fixing problems easier.
Reusability: Objects can be reused in different programs.

What are the fundamental concepts of object-oriented technology? Explain them.

Class – A class is a collection of data and operations on data. Data and operations/functions/methods are placed together in a single unit, i.e., class. This feature is known as encapsulation.

Objects – A class is like a blueprint of a building. An object is the building itself. Technically speaking, an object is the real entity of a specific class, which involves the real operations of an OOP application.

Inheritance: The properties of one class can be used by another class in the best way, and the class can be extended as the need may be. This feature is known as Inheritance.

What are the basic concepts of OOP?

The four basic concepts of OOP are:
a.) Abstraction
b.) Polymorphism
c.) Inheritance
d.) Encapsulation

What is dynamic or run-time polymorphism?

– It is also referred to as method overriding. Here, there can be two methods with same name and signature but different implementation.
– The function here is resolved during run time rather than compile time.

What is Inheritance?

– It is the process that allows the objects of one class to acquire the properties of objects of another class.
– The class that inherits is called sub-class while the class from which the object is inherited is called superclass.
– Inheritance helps in re-using the code and polymorphism.

Explain method overriding.

– When a subclass declares a method possessing similar arguments as a method declared by one of its superclass, method overriding takes place.
– Using this technique, the behavior specific to a particular subclass can be defined.
– The methods marked public, final, or static can not be overridden

Can you give some examples of tokens?

Some of the examples of tokens are:
– Keywords,
– Identifiers,
– Constants,
– Operators,
– Brackets,
– Commas.

What is the friend function?

– Friend function is a friend of a class.
– It is allowed to access Public, private or protected data of that class.
– It can be declared anywhere in the class declaration
– It doesn’t have any effect on access control keywords like private, public, or protected.

Define Modularity?

– It is the property of big a system divided into small modules which can be integrated as per the requirement.

Explain a.) Persistence. b.) Collaboration

a.) Persistence.
– It is the property of an object which extends its existence into space and time.

b.) Collaboration
– Process by which several objects cooperate to deliver a higher-level result.

What is a ternary operator?

– It is also called a conditional operator.
– It is an operator that can take three arguments.
– The data types of arguments and results are different.

What are sealed modifiers?

– Access modifiers cannot be inherited by other methods.
– They can be applied to properties, events, and methods but not to static members.

Explain a.) Static binding b.) Dynamic binding

a.) Static binding-
It is a binding in which the name of the class can be associated with it during compilation. Also referred to as early binding.

b.) Dynamic binding –
It is a binding in which the name of the class can be associated with it during execution time. Also referred to as late binding.

What are the different ways for a method to be overloaded?

A method can be overloaded by:
– Varying the numbers of parameters
– Using different data types for the parameters
– Using different sequences of the parameters.

What is composition? Explain the purpose of the composition.

Assembling existing components instead of creating new ones is called composition. In OOP it is called as objects composition. It is the process of placing an object in another object. It is the model of has-a relationship. An employee object can contain an object of type project which is another object.

Purpose of composition:
A model by value aggregation can be derived by using a composition that is semantically equivalent to an attribute.

The lifetime is a coincident part as a whole for both objects

If one part is removed, the whole part also removed without explicit removal of individual parts

The composition can be used to model by-value aggregation which is semantically equivalent to an attribute.

What is an abstraction and why is it important?

Representing essential features by hiding the background process/details. In other words, it is specifying what to do but not how to do.

Abstraction is important at the conceptual level of an application. It helps in understanding clearly, what the process and the flow of an application. The abstraction allows the complete flow and development of an application into a structured action. The conceptual level of project execution is derived from abstraction which the gateway for the entire application development.

How a program can be structured using the concept of Object-oriented programming?

The program can be structured by splitting the one big task into subtasks, creating some function for the tasks that have to be worked upon and then writing a program to instruct the computer to perform the desired calculations on the basis of which the output will be generated. As a large amount of data or tasks will be separated into less complex programs then it will be easier to manage. In an object-oriented program, the program structure is maintained according to the objects made up from the class. Every function is in a particular class that has an object calling certain properties and methods for implementation. It can manage the complexity of the large pieces and will be able to create a modular approach towards the programming methodology.

What are the features that are provided to make a program modular?

Creating a program requires self-sufficient resources, the way to make a piece of code modular so that it can be handled properly. This shows the relationship between different objects or in between the same objects. Different functions have to be used to keep the code different from the data provided. Object-oriented programming allows creating a modular approach to make it more abstract and create the interactions between them.
The features that are being provided in object-oriented programming is:
• Encapsulation: it deals with the grouping of data and functions together at one place or it can be said in an object that defines the interface of their interaction and the relationship between them.

• Inheritance: it deals with the relationship that exists between the parent and child classes. A child can inherit the properties of the parent and it remains helpful in creating a hierarchy in the system to keep things more modular.

• Polymorphism is a feature that deals with different values that can be used by only one function. It doesn’t have to re-create the same function again and again for different values but, it uses the same function to call different data types.

Write a program to show the inheritance used in a class.

Inheritance is a way to define the hierarchy of the related classes. It allows property sharing from one class to another class. It is an easy way to inherit the properties of the parent by the child and use the same properties again and again without redefining the class. The program is as follows it shows a class student that inherits the properties (methods+ data) from the teacher class.

class teacher
{
public:
t(){}
};class student : public teacher
{
public:
s(){}
};void use(teacher const& some)
{
some.t();
}

What is the function of pure virtual functions?

Pure virtual function in object-oriented programming is called a virtual method that acts as a function allowing its behavior to be overridden by the class that is inheriting the pure virtual function with the same signature. This is used in case of polymorphism. It is used when a base class is being driven by the derived class and an object of the derived class referred as base or derived class type. When a derived class overrides the base class method then the output or the behavior will be called as ambiguous. To use the virtual function a virtual keyword is used. This allows the function to be defined in every derived class and use the functionality of it.

What is the syntax of the object-oriented method call?

The object-oriented syntax tells about the object-oriented features and methodologies that are present and shown as:

target.method(arguments);
This is the line that can be used to call the functions, but not invoke the methods on an object. A function is made up of both the operands and operators and they are very essential to call a method. So, the method will be written as:

a = sub(c,b);
The object-oriented syntax allows easy-to-write ways and some specified rules that have to be remembered while programming. The operator has to always come in the middle of the statement. A class is made for every module and it also represents the template used for a class made up of objects.

What is the difference between data hiding and implementation?

– Data hiding is the concept of hiding the data from the other objects. It allows the data to be hidden from other objects that can prevent the use of any other objects. This way the direct manipulation of the object can’t be done and the cell will hide its internal mechanism of it. A method uses an interface such as primary, public, etc. The implementation keeps the separate data and lets the user implement the structure of the data that is being provided already.- Implementation allows the object to be changed according to the requirement. It deals with objects communication via messages in which when a target object then the implementation can be done with the method. The example is given below:

class teacher
{
// properties of the teacher
String name[];
int numb;// behavior
public void()
// this is the function that is given and it will include all your code
}

What are the properties that are defined in an object model?

Object-oriented programming always consists of an object model that includes state and behavior. The state defines the present condition of the system or an entity. The behavior includes the data and the operations that are performed on those data. The object represents the group of related functions and data structure that is used to give functionality to the functions. The functions that are being represented are the object models. It consists of the data structure, data type, and instance variables. Methods are used to hide the variables from the user and and define a high level in the object model. The object model also consists of the flow properties through which the object can be accessed with a defined relationship.

What is the function of messaging metaphor?

Object oriented programming is having its own metaphors that are associated with the program or the code that has a role to play in the program. Messaging metaphor represent the relationship between the actors that are involved it and the roles each are playing. This allows easy passing of the responsibilities and information to the processes that are in contact with the one which is passing the information. Messaging method allows the user to use the objects rather than their functions. As, the objects perform all the actions that is been done by the methods or the functions alone. Objects consists of state and behavior so they are not active rather passive, but they act as an agent to allow the program’s activity to be performed easily. This metaphor keeps all the objects separate each with the defined roles.

Why is message passing between the objects important?

Objects use the metaphor concept to pass the messages between different objects. The objects communicate through the messages only. The first step is to call the method as the functions are called in a normal way. The moment a function is called by an object a message will be passed to all the objects to allow the operations to be performed. Then the abstract method is separated from the particular data to show the correct behavior of the state. Object oriented programming keeps a start function that initiates the operation. Then the information that is contained in the object is archiving and then the program gets executed according to the method or the function. The different objects will have different functions to be performed. There are few abstract behaviors and to make it concrete the method has to be associated with an object.

What is the main use of message metaphor in object-oriented programming?

Methods belong to objects and they are invoked by using a particular receiver only. The receiver can be either owner of method or the data structure whose method will be. The receivers can have different implementation that can be done for the same method. Different receivers can also perform different operations and produce different responses in case of the same message. The result of the message will also depend on the object that is receiving the message. The message or the request can be separated from the receiver who is the owner of the function that is being called to capture the behavior of the abstract data type and implement the function properly.

Why is class hierarchies managed in object-oriented programming?

Class is used to store some methods and behavior. Class is used to access through an object and create a relationship between all the subclasses. A class can be made a super class of another classes that are present will be called as the subclass of it. Many classes can be linked together in a hierarchy of inheritance. The inheritance hierarchy consists of a root class and this is also called as the super class. The root class hierarchy sends the branch downwards. This class inherits the features from the super class and from all the other classes that are at the top level in the hierarchy. Each class consists of the class definition and the properties that are inherited from other classes. Every class consists of one super class and can consist of any number of subclasses.

What are the methods required to create changes in Subclasses?

– Subclass is a class that is under the super class and it inherits the property of the subclass as well. The class definition can be expanded by using the class definition that inherits the methods and variables that are used in the program. The subclasses consist of their own methods and variables with the super class variables as well.
The methods that are used:
– Subclass can modify the behavior that it inherits from the existing method.
– Subclass can extend the behavior of the object by inheriting the new methods and functionalities. Subclass overrides any method that is being taken from the super class.
– Subclass fills the super class properties to make it more specific and specialized. There is addition of program or code take place and the replacement occurs only at the time of new functionalities coming up.

What is the function of dynamic typing?

Dynamic typing is a way to allow the compiler to replace an existing value with a type that is not functioning properly. There can be warning signs like: incompatible types in assignment. This warning sign shows that there is type checking that casts the object from one to another to make it compatible with the current system. The dynamic typing checks for the type of object that is being during the compile time and during the run time the value doesn’t change. If the class of the variable can be found during the run time then it will be possible to find out the class of the variable. Dynamic binding provides the output to the dynamic binding. It allows the binding between the objects to be done at runtime.

Why dynamic binding is used in object-oriented programming?

Dynamic binding allows delaying the decision of running the program. Dynamic binding is used to perform messaging transparently and routinely by allowing different objects to be binded on the run time. It allows the declared pointer to find out the assigned values of a give procedure. Messages that are given with the programs are invoked indirectly. Every method has a message expression that has to be found for implementation. The class of the receiver is checked to locate the implementation of the method that is mentioned in the message. When at run time the method is run then the complier dynamically bind the objects.The example shows the dynamic binding of the object:

int strcmp(const char *, const char *);

int strcasecmp(const char *, const char *);

int (* compare)(const char *, const char *);

if ( **argv == 'i' )

compare = strcasecmp;

else

compare = strcmp;

What is the purpose of late binding in object-oriented programming?

Late binding is done at the run time and it requires the messages to be passed to the receiver statically by writing in the code or the program. An object can be attached to its own class or any class that inherits the properties of the class. The compiler has difficulty in understanding whether the source is specified in the type declaration or not. As, if an object is given then on run time it is not possible for the compiler to know its class then for that the instance of the specified class is binded with the method that is defined for that particular class to the messages. The late binding is done during the linking of the method to the procedure of the program. It consists of strict compile-time rules that put constraints on the program in execution.

What are the major differences between late and dynamic binding?

– Late binding allows the rules to be set up during the compilation time only, whereas the dynamic binding allows the methods to be dynamically bound together with the function at run time only.- Late binding consists of some constraints strictly on the basis of compile-time, whereas dynamic binding is unconstrained.- Late binding doesn’t exist with dynamic binding, whereas dynamic binding can exist with dynamic typing.- Dynamic binding allows the code that is written to send the messages to the objects, whereas late binding just show the relationship between the sender and receiver.

Why dynamic loading is used in object-oriented programming?

Dynamic loading is required to load the object or class when the demand for it rises. Before the loading in the linking phase all the links of the objects that are linked together, gets contained in one file. Dynamic loading loads the entire environment to be loaded at once. It allows different parts of an executable program to be given in different files. Each piece in the program is dynamically loading and some user actions can be performed on the software. It focuses on the programs that are in the memory. Large programs are always required to be loaded at start. The modules can be dynamically added. The advantage of this is that an entire program doesn’t require a single feedback. It allows the extensibility of the program that has to be done to make an application.

Why are Outlet Connections required in object-oriented programming?

The object network is arranged using the design of object-oriented programming. The network is having dynamic requirements and can’t remain static at any time while running a program. The network has to maintain a relationship between the objects and some roles are assigned from time to time using a script. Outlet connections depend on the message that is passed between the objects. Messages are used to identify an object and it is usually used for communication with the receiver. The messages have to be recorded in the database using the object connections. There can be made some instances to keep the track of the objects that communicates with one another. The outlet connections record the messages and store them on the program network. The objects are having the four outlets like an agent, a friend, neighbor and a boss, and the roles are interchanged from each other.

What are Extrinsic and Intrinsic Connections in object-oriented programming?

There are different objects that are part of one another. These objects have intrinsic and extrinsic properties that are applied. An object keeps other objects in the list of processes. There are some building objects that have a list of all the objects that are used in the program. The objects that are used belong to building objects. The extrinsic behavior comes when one object communicates with another object. Intrinsic outlets are different and they are used when an object is about to be freed or archived in a file. The archived message has to be kept in a file; these files are dependent on the program subcomponents. Extrinsic outlets allow the capture of the program for an organization at a higher level and then the connection-related settings to be recorded and stored using the independent program concept.

What is the difference between Aggregation and composition?

Aggregation is a collection of the entire program that consists of only one object and this object sends messages to itself and other objects by using the method of polymorphism. The modularity concept is used for the classes and program design to set the network of objects that are interconnected to each other. In this, the program is hidden from the class definition. Composition on the other hand is a way to combine all the small sub-components to provide the functionalities in a modular format. Doing this will make the structure less usable. The objects in this can be made part of another in this way the object only exists not anything else associated with an object.

In conclusion, being familiar with OOP concepts and principles is essential for anyone preparing for an oop interview questions in software development. The questions and answers provided here cover some of the most common topics in OOP interview questions, but it’s important to do additional research and practice coding exercises to strengthen your OOP skills. With the right preparation and practice, you can ace your OOP interview questions and land your dream job in software development. Hope this OOP interview question helps you for interviews!

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