Important OOPS Interview Question

Q-1 What is meant by Object Oriented Programming? 

       OOP is a method of programming in which programs are organized as cooperative

       collections of  objects. Each object is an instance of a class and each class belong to

       a hierarchy.

Q-2 What is an Instance? 

      An instance has state, behavior and identity. The structure and behavior of similar 

      classes are defined in their common class. An instance is also called as an object. 

Q-3 What is a Class? 

     Class is a template for a set of objects that share a common structure and a common behavior. 

Q-4 What are the core OOP’s concepts? 

    Abstraction, Encapsulation, Inheritance and Polymorphism are the core OOP’s concepts.

Q-5 What is a base class?

     Base class is the most generalized class in a class structure. Most applications have

     such root classes. In Java, Object is the base class for all classes. 

Q-6 What is a constructor? 

    Constructor is an operation that creates an object and/or initializes its state. 

Q-7 What is a destructor? 

    Destructor is an operation that frees the state of an object and/or destroys the object itself. 

    In Java, there is no concept of destructors. It’s taken care by the JVM. 

Q-8 What is a subclass? 

    Subclass is a class that inherits from one or more classes. 

Q-9 What is a superclass? 

   Superclass is a class from which another class inherits. 

Q-10 What is an Object?

   Object is an instance of a class. It has state, behaviour and identity. It is also called as an 

   instance of a class. 

Q-11 What is collaboration? 

    Collaboration is a process whereby several objects cooperate to provide some higher 

    level behavior. 

Q-12 What is meant by Binding? 

    Binding denotes association of a name with a class 

Q-13 What is meant by Dynamic binding? 

    Dynamic binding is a binding in which the class association is not made until the object is 

    created at execution time. It is also called as late binding. 

Q-14 What is meant by Encapsulation? 

    Encapsulation is the process of compartmentalizing the elements of an abstraction

    that defines the structure and behavior. Encapsulation helps to separate the contractual

    interface of an abstraction and implementation. 

Q-15 What is meant by Inheritance? 

    Inheritance is a relationship among classes, wherein one class shares the structure or 

    behavior defined in another class. This is called Single Inheritance. If a class shares the

    structure or behavior from multiple classes, then it is called Multiple Inheritance. 

    Inheritance   defines “is-a” hierarchy among classes in which one subclass inherits from

    one or more generalized superclasses. 

Q-16 What is meant by Persistence?

    Persistence is the property of an object by which its existence transcends space and time. 

Q-17 What is meant by Polymorphism? 

    Polymorphism literally means taking more than one form. Polymorphism is a

    characteristic of being able to assign a different behavior or value in a subclass,

    to something that was declared in    a parent class. 

Q-18 What is meant by abstraction? 

   Abstraction defines the essential characteristics of an object that distinguish it from all other 

   kinds of objects. Abstraction provides crisply-defined conceptual boundaries relative to

   the perspective of the viewer. It’s the process of focusing on the essential characteristics 

   of an object. Abstraction is one of the fundamental elements of the object model. 

Q-19 What is meant by static binding? 

   Static binding is a binding in which the class association is made during compile time. 

   This is also called as early binding.  

Q-20 What is an Interface?

   Interface is an outside view of a class or object which emphasizes its abstraction while 

   hiding its structure and secrets of its behavior.