should MAIN method copy input arguments?

Question

Can someone imagine when this code:

public static void main(final String[] args) {
   // do something
}

should become this:

public static void main(final String[] args) {
   String[] argsCopy = doCopy(args);
   // do something
}

(In our company we have a Sonar rule that forces such coping or arguments for all methods.) I can imagine why it can be important for standard methods, but I cannot find any benefit of having it done at a start of tools main method. Am I missing something?

Answer 1

I can imagine quite a bit, the two most obvious (to me) are:

• If you modify them but still need to refer to the original values
• If you use main as a "normal" method, e.g., not just called from the command line

In general, though, it's not super-useful in this case.

Answer 2

The reason you copy array parameters is to avoid a possibility of someone modifying the array once you have validated its elements. This is a very good defensive technique, which protects you from malicious calls in a caller.

However, in this case the caller is JVM itself. If you do not trust JVM to be free of malicious code, you have a much larger problem than something that could be solved by copying an array.

The only exception is when you pass args to some of your functions. In this case, making a copy is a very good idea, in case some method decides to change the content of the args. That's the only case when I would recommend making a copy. If main is the only place where args is used, making a copy is not necessary.