Modifying a main method to take a text file when compiling the java file

Question

How can I make a main method take a text file as an argument on the command line?

So for example

java ClassWithMainMethod textFileNeededInMainMethod.txt

I've been told this is possible but I'm not sure how it's done.

Answer 1

You use the String[] args from the Java program entry point like

public static void main(String[] args) {
  if (args.length < 1) {
    System.err.println("no file provided");
    System.exit(1);
  }
  File f = new File(args[0]);
  // ...
}

That if could be used to set a default file if one isn't provided. Finally, it's a good idea to use File.canRead() before you try and read from a file.

Answer 2

The arguments passed to main are of type string so you'd pass the name of the file or path of the file and then create a file object and then read its content.

You can't pass the type file to a java main class

Answer 3

In your main method, the args array contains any arguments. For example, if you typed java ClassWithMainMethod textFileNeededInMainMethod.txt , then you could read the argument like this:

public static void main(String[] args) {
    String file = "";
    if(args.length > 0) file = args[0];
}