Here are 20 basic Java interview questions and answers:
1. What is Java?
Answer: Java is a high-level, object-oriented programming language used for developing applications and software.
2. What is the difference between a class and an object?
Answer: A class is a blueprint for creating objects, while an object is an instance of a class.
3. What is a constructor in Java?
Answer: A constructor is a special method that is called when an object is created. It is used to initialize the object's variables and allocate memory.
4. What is inheritance in Java?
Answer: Inheritance is a mechanism in which one class inherits properties and methods of another class.
5. What is polymorphism in Java?
Answer: Polymorphism is the ability of an object to take on many forms. In Java, polymorphism is implemented through method overloading and method overriding.
6. What is method overloading in Java?
Answer: Method overloading is when two or more methods have the same name but different parameters.
7. What is method overriding in Java?
Answer: Method overriding is when a subclass provides its own implementation of a method that is already defined in its superclass.
8. What is an interface in Java?
Answer: An interface is a collection of abstract methods that can be implemented by classes.
9. What is an abstract class in Java?
Answer: An abstract class is a class that cannot be instantiated, but is instead used as a base class for other classes.
10. What is a package in Java?
Answer: A package is a collection of related classes and interfaces.
11. What is a static variable in Java?
Answer: A static variable is a variable that belongs to the class and not to any instance of the class.
12. What is a final variable in Java?
Answer: A final variable is a variable that cannot be changed once it is initialized.
13. What is a static method in Java?
Answer: A static method is a method that belongs to the class and not to any instance of the class.
14.What is a final method in Java?
Answer: A final method is a method that cannot be overridden by a subclass.
15. What is the difference between public, private, and protected access modifiers in Java?
Answer: Public methods and variables can be accessed from anywhere, private methods and variables can only be accessed within the class that defines them, and protected methods and variables can be accessed within the class and any subclasses.
16. What is a try-catch block in Java?
Answer: A try-catch block is used to handle exceptions in Java.
17. What is a NullPointerException in Java?
Answer: A NullPointerException occurs when a program attempts to use an object reference that is null.
18. What is a stack overflow error in Java?
Answer: A stack overflow error occurs when a program's call stack exceeds its maximum size.
19. What is the difference between an ArrayList and a LinkedList in Java?
Answer: An ArrayList is a dynamic array, while a LinkedList is a linked list.
20. What is a lambda expression in Java?
Answer: A lambda expression is a function that can be created without a formal definition and can be passed as an argument to other methods or functions.
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