22 Mar, 2024
Oops Concepts Interview Questions In Java
Commonly Asked Java OOP Interview Questions
Object-oriented programming (OOP) is a popular programming approach that focuses on creating objects and using them to build applications. In Java, OOP concepts are at the core of the language, making it essential for developers to have a good understanding of these concepts. Some common OOP interview questions in Java may include questions about the four key principles of OOP (abstraction, encapsulation, inheritance, and polymorphism) and how they are implemented in Java, as well as questions about classes, objects, interfaces, and their relationships. Interviewers may also ask about key concepts such as inheritance, method overriding, and overloading. It is important for candidates to have a thorough understanding of OOP principles and how they are applied in Java to successfully answer these interview questions.
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1 - What is the main difference between an abstract class and an interface?
- An abstract class can have both abstract and non-abstract methods, while an interface can only have abstract methods.
- - An abstract class can have constructors, while an interface cannot.
- - A class can implement multiple interfaces, but can only extend one abstract class.
- 2) What is encapsulation?
- - Encapsulation is the concept of bundling data and methods together within a class, and protecting the data from being accessed directly outside the class. This allows for better control over the data and ensures that it is accessed and modified in a controlled and secure manner.
- 3) Explain the concept of inheritance.
- - Inheritance is the process of acquiring the properties and behavior of a parent class by a child class. This helps in promoting code reusability and allows for the creation of more specialized classes with their own unique features.
- 4) What are the types of inheritance in Java?
- - Single inheritance: when a child class inherits from only one parent class.
- - Multilevel inheritance: when a child class inherits from a parent class, which in turn inherits from a grandparent class, and so on.
- - Hierarchical inheritance: when multiple child classes inherit from one parent class.
- - Multiple inheritance (not supported in Java): when a child class inherits from more than one parent class.
- 5) Can you have multiple inheritance in Java? If not, how does Java achieve code reuse?
- - No, Java does not support multiple inheritance. Java achieves code reuse through interfaces, which allow classes to inherit from multiple interfaces while avoiding the issues of multiple inheritance.
- 6) What is the difference between a static and non-static method?
- - A static method belongs to the class itself and can be accessed without creating an instance of the class. Non-static methods can only be accessed through an instance of the class.
- - Static methods cannot access non-static methods or variables directly, while non-static methods can access both static and non-static methods and variables.
- 7) What is a constructor?
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- - A constructor is a special method used to initialize objects, allocate memory, and set default values for variables in a class. It has the same name as the class and is automatically called when an object of the class is created.
- 8) How is method overloading different from method overriding?
- - Method overloading is the creation of multiple methods with the same name but different parameters within the same class. This allows for different variations of the same method to be called based on the arguments passed in.
- - Method overriding is the redefinition of a method in a child class with the same name and parameters as a method in the parent class. This allows for the child class to have its own implementation of the method.
- 9) What is the difference between a shallow copy and a deep copy?
- - A shallow copy creates a new object with the same values as the original object, but the new object still references the original object's variables. This means that changes made to one object will affect the other.
- - A deep copy creates a new object with its own separate copy of all values, both primitive and object type. This ensures that changes made to one object do not affect the other.
- 10) What is an abstract method?
- - An abstract method is a method without a body, marked with the keyword “abstract”. It must be defined in an abstract class or interface and implemented in a child class. It serves as a placeholder for a method that must be implemented in the child class.
- 11) What is a final class?
- - A final class is a class that cannot be inherited by any other class. It cannot have any child classes. Usually, the purpose of making a class final is to prevent any modifications to its behavior.
- 12) What is the difference between a final method and a final class?
- - A final method is a method that cannot be overridden in any child class. It is used to prevent modification of behavior in a method.
- - A final class is a class that cannot be inherited by any other class, making it unable to have any child classes. This is used to prevent any modification of behavior in the entire class.
- 13) What is polymorphism?
- - Polymorphism is the ability of an object to have multiple forms. This allows it to be used and interpreted differently depending on the context it is used in. In Java, polymorphism is achieved through method overloading and method overriding.
- 14) What is the difference between shallow copying and deep copying of objects?
- - Shallow copying creates a new object with the same values as the original object, but the new object still references the original object's variables. This means that changes made to one object will affect the other.
- - Deep copying creates a new object with its own separate copy of all values, both primitive and object type. This ensures that changes made to one object do not affect the other.
- 15) What is the role of the “this” keyword in Java?
- - The “this” keyword refers to the current object instance within a class. It is used to access instance variables, methods, and constructors of the current object. It is also used to avoid naming conflicts between local variables and instance variables within a method.
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