Thread: New to Java

Hi, Im new to java, coming from C++, and i had a question about the first line of code.

 public static void main(String[] args)

in the code i understand public static void main, but i dont understand what is in the brackets. What are they for, and would i need to change them for a code that didnt just print out "hello world"?
Thanks

Lesson: A Closer Look at the "Hello World!" Application (The Java™ Tutorials > Getting Started)

Read carefully the part about 'signature'. The JVM needs to know whereabouts in your application to start executing code, so the standard is that it loads the class you tell it to and invokes main(String[]), passing command-line arguments as a String array.

If you're up to a coding challenge, change HelloWorldApp in the link above to say "Hello [whatever]" where "[whatever]" is a command-line argument. That is, if you start HelloPottsiex5App like this:

java HelloPottsiex5App coders

It should print the message:

Hello coders!

Hey, Im still a little confused. When you say a command-line arguement, is that the same as parameters? And if it is, then i still dont understand how the parameters of function main can be the String[]... What did you mean it passes command-line arguements as a String array?

Do you ever run java applications from the command line by typing "java MyApplication"? If you don't, this is going to be a tortuous explanation.

Oh you mean using the command promt/terminal? I dont regularly run them in there, but i think i understand what you mean now. So if i were to run it in the command prompt or terminal and i were to use "java MyApplication" and then add "[whatever]" on to that then i could have the input of a variable be the [whatever]?
I remember something like that from batchfiles...

then i could have the input of a variable be the [whatever]?

Yes, like that, but it only works in the special case of the main(String[] argumentsArray) method. When the JVM starts, it takes whatever is on your commandline after the name of the class to load and turns those strings into a String[], which it then passes to the main(String[]) method.

Say for example you type at the command prompt:

java MyAddingApp 2 2

What the main method sees in its String[] argument (you can give it any name you like, args is only a Java programmer habit) is the same as if some other code had invoked your main method like this:

MyAddingApp.main(new String[]{"2", "2"});

and you can access the command arguments like this:

System.out.println(args[0] + " + " + args[1] + " = something");

which would print

2 + 2 = something

You can add the "2"s like this to make a longer string because they're strings. To make them into integers (int, probably), you'd have to explicitly convert them first.

Awesome

So for your challenge it would be this

public class CommandLineTest
{
    public static void main (String[] args)
    {
        System.out.println ("Hello, " + args[0]);
    }
}

?

?

I'm assuming - since that looks like valid Java - you know the answer already

That's right.