Java Interview Questions
Here are some common Java interview questions with answers:
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.