What is “String args[]”? parameter in main method Java

Question

I\'m just beginning to write programs in Java. What does the following Java code mean?

public static void main(String[] args)

• What

Answer 1

I would break up

public static void main(String args[])

in parts.

"public" means that main() can be called from anywhere.

"static" means that main() doesn't belong to a specific object

"void" means that main() returns no value

"main" is the name of a function. main() is special because it is the start of the program.

"String[]" means an array of String.

"args" is the name of the String[] (within the body of main()). "args" is not special; you could name it anything else and the program would work the same.

• String[] args is a collection of Strings, separated by a space, which can be typed into the program on the terminal. More times than not, the beginner isn't going to use this variable, but it's always there just in case.

Answer 2

In Java args contains the supplied command-line arguments as an array of String objects.

In other words, if you run your program as java MyProgram one two then args will contain ["one", "two"].

If you wanted to output the contents of args, you can just loop through them like this...

public class ArgumentExample {
    public static void main(String[] args) {
        for(int i = 0; i < args.length; i++) {
            System.out.println(args[i]);
        }
    }
}

Answer 3

args contains the command-line arguments passed to the Java program upon invocation. For example, if I invoke the program like so:

$ java MyProg -f file.txt

Then args will be an array containing the strings "-f" and "file.txt".

Answer 4

The String[] args parameter is an array of Strings passed as parameters when you are running your application through command line in the OS.

So, imagine you have compiled and packaged a myApp.jar Java application. You can run your app by double clicking it in the OS, of course, but you could also run it using command line way, like (in Linux, for example):

user@computer:~$ java -jar myApp.jar

When you call your application passing some parameters, like:

user@computer:~$ java -jar myApp.jar update notify

The java -jar command will pass your Strings update and notify to your public static void main() method.

You can then do something like:

System.out.println(args[0]); //Which will print 'update'
System.out.println(args[1]); //Which will print 'notify'

Answer 5

In addition to all the previous comments.

public static void main(String[] args) 

can be written as

 public static void main(String...arg)

or

 public static void main(String...strings)

Answer 6

When a java class is executed from the console, the main method is what is called. In order for this to happen, the definition of this main method must be

public static void main(String [])

The fact that this string array is called args is a standard convention, but not strictly required. You would populate this array at the command line when you invoke your program

java MyClass a b c

These are commonly used to define options of your program, for example files to write to or read from.