Java Language Interview Questions

1. Class: 

        A blueprint or template for creating objects that define their state and behavior.


2. Object: 

        An instance of a class that has its own state (fields) and behavior (methods).


3. Method:

         A block of code that performs a specific task. Methods define the behavior of objects.


4. Constructor: 

        A special method used to initialize objects. It has the same name as the class and is called automatically when an object is created.


5. Inheritance:

         The mechanism by which one class (subclass) acquires the properties and behaviors of another class (superclass). It promotes code reuse.


6. Polymorphism: 

        The ability of an object to take on different forms. In Java, it allows methods to be overridden in subclasses to provide different implementations.


7. Encapsulation: 

        The bundling of data and methods that operate on that data into a single unit (class). It hides the internal state of an object from the outside world.


8. Abstraction:

         The concept of hiding the complex implementation details and showing only the essential features of an object. Abstract classes and interfaces are used to achieve abstraction.


9. Interface:

         A reference type in Java that defines a set of abstract methods. It is similar to a class but cannot contain implementation code. Classes can implement interfaces to provide specific behavior.


10. Package: 

        A namespace that organizes a set of related classes and interfaces. It helps in avoiding naming conflicts and provides access protection.


11. Variable: 

        A container that holds data, such as primitive types or references to objects. Variables have a type, name, and value.


12. Primitive Data Type: 

        The most basic data types available in Java, such as int, double, boolean, char, etc. They are not objects and are stored directly in memory.


13. Reference Data Type:

             Data types that refer to objects. They store references or addresses of objects in memory rather than the actual object data.


14. Static Keyword: 

            A keyword used to define class-level variables and methods. Static members belong to the class rather than individual objects and can be accessed without creating an instance of the class.


15. Final Keyword: 

        A keyword used to restrict the behavior of classes, methods, and variables. It can make a class not extendable, a method not overrideable, or a variable unchangeable.


16. Access Modifier: 

        A keyword used to control the accessibility of classes, methods, and variables in Java. Common access modifiers include public, private, protected, and default.


17. Method Overloading:

         The ability to define multiple methods in a class with the same name but different parameters.


18. Method Overriding: 

        The ability of a subclass to provide a specific implementation of a method that is already defined in its superclass.


19. Abstract Class:

         A class that cannot be instantiated and may contain abstract methods. It is meant to be subclassed to provide specific implementation details.


20. Abstract Method:

         A method declared without an implementation in an abstract class. Subclasses must provide an implementation for abstract methods.

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21. Interface Implementation: 

        The process of implementing the abstract methods defined in an interface in a concrete class.


22. Package Visibility:

         The default access level of a class, method, or variable if no access modifier is specified. It allows access only within the same package.


23. Casting: 

        The process of converting a value from one data type to another in Java. It can be either implicit or explicit.

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24. Wrapper Class:

         A class in Java that provides an object representation of primitive data types. It allows primitive data types to be used as objects.


25. Exception Handling: 

        The process of handling errors or exceptional situations that occur during the execution of a program. It helps in preventing program crashes and providing graceful error recovery.

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