What is main in Java - why public static and void (original) (raw)

main method in Java is an standard method from which execution of any core java program starts. when we run Java using "java" command we provide name of Class which contains standard public static void main(String args[]) method and after loading that class JVM calls this main method to start execution of Java application. Java program runs until main method is finished or any user thread created from main method is live and terminates normally when main method finished in a single thread application and when all user thread finished in a multi-threaded application. By the way this is not the first article in Java fundamentals you can also see What is PATH and CLASSPATH in Java and Difference between String and StringBuffer to learn more about fundamental topics in Java programming language.

main method is one of the fundamental things to know about Java programming language, if you are coming from C or C++ background than you must be familiar with name main() as that is also the starting point for any C and C++ application but main method in C or C++ is very different than main method in Java like return type of C and C++ main method is int while return type of Java main method is void, not just that main method in Java is public, static and void in Java and it also accept String array as argument. If you declare main method with any other signature than standard main method than JVM will not recognize that you will not be able to run your Java program and likely to get error like "no main method is found". By the way from Java 5 onwards you can also use variable arguments to replace String array as argument in Java. for example following two signature of main method is acceptable :

Signature of main method in Java

public static void main(String argument[]) and

public static void main(String... argument)

three dots at the end of String denotes variable arguments in Java.

Why main method is public static and void in Java

Since we know that main is public, static and void in Java but why? this is one of the tricky Java interview question which appears now and then in any Java interviews. let's see Why main is public, static and void in Java.

main method in Java is public so that its visible outside the class its declared. you can also see this article which discusses this topic in more detail Why main is public static and void in Java

main method is static so that it can be invoked without creating instance of the class as at the time of calling main method, JVM doesn't know how to create instance of the class which holds main method i.e. if that class contains multiple constructor than calling which constructor ?

main method is void because its not expected to return anything to JVM, main method runs under JVM and invoked by JVM not directly by operating system.

That is all about main method in Java, we have seen What is main method in Java, What is signature of main method and Why main in Java is public,static and void in Java. If you come across any other reason about main being public, static and void then post as comment.