CODEWITHSUNDEEP
java
amit
amit

Reputation: 119

Why main() method is needed in java main class

I know we can compile and run a java program successfully without a main() method, but why we still need main() method in java's main class?

Upvotes: 11

Views: 45893

Answers (6)

Santosh
Santosh

Reputation: 17903

Quoting Java Language Specification (JLS)

A Java virtual machine starts execution by invoking the method main of some specified class, passing it a single argument, which is an array of strings.

Now a typical definition of main method from which execution start is

public static void main(String[] args)

public - accessible from anywhere

static - accessible statically, meaning without an instance (as JVM starts, it has no instance of the class containing main method, hence static).

void - returns void.

So calling the main() method is 'hardcoded' in JVM as the starting point.

Upvotes: 7

Esann
Esann

Reputation: 77

  1. To answer this we need to understand the fantastic Java architecture.
  2. We have Java source code (.java file)
  3. Compiler checks for errors and generates byte code as the .class file
  4. Then class loader loads .class file

  5. After that JVM takes the responsibility

    • a) JVM loads static blocks

    • b) After that, interpreter in JVM wants to read the code. In the bunch of code where to start reading is the question for JVM?

    • Answer: To solve this problem we are giving the main keyword as a clue for the JVM to start execution in this method.

  6. After that Java will produce output by dealing with the operating system and hardware
  7. Is my answer is clear enough? If there are any doubts, please comment.

Upvotes: 2

Massimiliano Peluso
Massimiliano Peluso

Reputation: 26737

Every Java application must contain a main method whose signature looks like this:

   public static void main(String[] args)

How the main Method Gets Called

The main method in the Java language is similar to the main function in C and C++. When the Java interpreter executes an application (by being invoked upon the application's controlling class), it starts by calling the class's main method. The main method then calls all the other methods required to run your application.

If you try to invoke the Java interpreter on a class that does not have a main method, the interpreter refuses to compile your program and displays an error message similar to this:

 In class NoMain: void main(String argv[]) is not defined

Arguments to the main Method

As you can see from the following code snippet, the main method accepts a single argument: an array of elements of type String.

   public static void main(String[] args)

This array is the mechanism through which the runtime system passes information to your application. Each String in the array is called a command-line argument. Command-line arguments let users affect the operation of the application without recompiling it. For example, a sorting program might allow the user to specify that the data be sorted in descending order with this command-line argument:

    -descending

for more info

http://journals.ecs.soton.ac.uk/java/tutorial/getStarted/application/main.html

Upvotes: 12

Smar
Smar

Reputation: 8601

main() is the starting point of an application. When application launches, this function is what is very first evaluated from your code. It is responsible of running your application.

Upvotes: 1

Joachim Sauer
Joachim Sauer

Reputation: 308041

You can compile any Java class without a main method, but a standalone application can't run without a main() method *.

The main method is the method that's defined to be called at the start of an application. Without it, there is no place to start running.

* well, there are ugly hacks where you can do it, but that's cheating

Upvotes: 5

Caner
Caner

Reputation: 59178

When a program starts running, it has to start execution from somewhere. That somewhere is called main.

Upvotes: 7

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