When do you use varargs in Java?

Question

I\'m afraid of varargs. I don\'t know what to use them for.

Plus, it feels dangerous to let people pass as many arguments as they want.

What\'s an example

Answer 1

I use varargs frequently for outputting to the logs for purposes of debugging.

Pretty much every class in my app has a method debugPrint():

private void debugPrint(Object... msg) {
    for (Object item : msg) System.out.print(item);
    System.out.println();
}

Then, within methods of the class, I have calls like the following:

debugPrint("for assignment ", hwId, ", student ", studentId, ", question ",
    serialNo, ", the grade is ", grade);

When I'm satisfied that my code is working, I comment out the code in the debugPrint() method so that the logs will not contain too much extraneous and unwanted information, but I can leave the individual calls to debugPrint() uncommented. Later, if I find a bug, I just uncomment the debugPrint() code, and all my calls to debugPrint() are reactivated.

Of course, I could just as easily eschew varargs and do the following instead:

private void debugPrint(String msg) {
    System.out.println(msg);
}

debugPrint("for assignment " + hwId + ", student " + studentId + ", question "
    + serialNo + ", the grade is " + grade);

However, in this case, when I comment out the debugPrint() code, the server still has to go through the trouble of concatenating all the variables in every call to debugPrint(), even though nothing is done with the resulting string. If I use varargs, however, the server only has to put them in an array before it realizes that it doesn't need them. Lots of time is saved.