Java Developer interview questions

JVM is an engine that provides runtime environment to drive Java applications or applets. It converts Java bytecode into machine language. JVM is a part of JRE (Java Runtime Environment). It's important because it provides a platform-independent way to execute code.

JDK (Java Development Kit) is a software development environment used to develop Java applications and applets. JRE (Java Runtime Environment) is a set of software tools for development of Java applications. JVM (Java Virtual Machine) is an engine that converts the bytecode into machine code. JDK includes both JRE and JVM.

Java features include platform independence, object-oriented, secure, architecture-neutral, portable, robust, multi-threaded, and high performance.

Java achieves platform independence by compiling Java code into bytecode. This bytecode can run on any machine that has a JVM, which is specific to each operating system.

The 'main' method is the entry point for any standalone Java application. Java Virtual Machine calls the 'main' method of the class which is passed as a parameter, hence it is always public static void and takes a single argument, an array of Strings.

An abstract class can have methods with default behavior and instance variables. Interfaces cannot have any method implementation (prior to Java 8). Abstract classes can provide some methods with implementation whereas interfaces can only declare methods.

Java provides a robust mechanism to handle runtime errors, with the use of try, catch, throw, throws, and finally blocks. Exceptions are objects that are thrown at runtime when an abnormal computation arises.

The 'final' keyword can be used with variables to make them constants, with methods to prevent them from being overridden, and with classes to prevent them from being subclassed.

A package in Java is a namespace that organizes a set of related classes and interfaces. It provides access protection and removes naming collision.

Garbage collection in Java is the process by which the JVM automatically removes objects that are no longer needed in order to reclaim and reuse their memory. Java's garbage collector works in the background, finding unused objects and marking them for removal.