Java Interview Questions

Here are some common Java interview questions with answers:

1. What is the Java Virtual Machine (JVM) and how does it work?

The Java Virtual Machine (JVM) is a software platform that allows Java programs to run on any device that has a JVM installed. It is responsible for executing Java bytecode, which is the compiled form of a Java program. The JVM interprets the bytecode and executes the instructions on the host machine.

2. What is the difference between an interface and an abstract class in Java?

An interface is a type that defines a set of abstract methods that must be implemented by any class that implements the interface. An abstract class is a class that cannot be instantiated and must be extended by a subclass. An abstract class can contain both abstract and non-abstract methods, whereas an interface can only contain abstract methods.

3. What is the difference between a static and a non-static method in Java?

A static method is a method that is associated with the class itself, rather than with a specific instance of the class. It can be called directly on the class, without the need to create an instance of the class. A non-static method, on the other hand, is associated with a specific instance of the class and can only be called on an instance of the class.

4. What is the difference between a primitive type and a reference type in Java?

A primitive type is a type that represents a single value, such as an integer or a boolean. A reference type is a type that refers to an object, which is a collection of data and methods.

5. What is an exception in Java, and how do you handle exceptions in your code?

An exception is an abnormal event that occurs during the execution of a program and disrupts the normal flow of the program's instructions. In Java, exceptions are represented by objects that are instances of the Exception class or a subclass of Exception. Exceptions can be handled in Java using a try-catch block, which allows the program to catch and handle the exception, or a try-with-resources block, which automatically closes resources that are opened in the try block.

6. What is the difference between a try-catch block and a try-with-resources block in Java?

A try-catch block is used to catch and handle exceptions that may be thrown during the execution of a program. A try-with-resources block is similar to a try-catch block, but it also automatically closes any resources that are opened in the try block, such as streams or connections.

7. What is a Java thread and how does it work?

A Java thread is a separate execution path that can run concurrently with other threads in a Java program. Threads are used to improve the performance of a program by allowing it to perform multiple tasks concurrently. A Java program can create and start a new thread using the Thread class or by implementing the Runnable interface.

8. What is the difference between a runnable and a callable in Java?

A Runnable is an interface that represents a task that can be executed by a thread. A Callable is similar to a Runnable, but it can return a value and throw a checked exception.

12. What is polymorphism in Java and how does it work?

Polymorphism is the ability of a single object to take on multiple forms. In Java, polymorphism is achieved through inheritance and the use of abstract classes and interfaces. A subclass can override the methods of its superclass, which allows it to behave differently when the same method is called on it. This allows a Java program to treat objects of different types in a uniform manner.