java - Is it problematic to assign a new value to a method parameter?

Question

Eclipse has an option to warn on assignment to a method's parameter (inside the method), as in:

public void doFoo(int a){
   if (a<0){
      a=0; // this will generate a warning
   }
   // do stuff
}

Normally I try to activate (and heed) almost all available compiler warnings, but in this case I'm not really sure whether it's worth it.

I see legitimate cases for changing a parameter in a method (e.g.: Allowing a parameter to be "unset" (e.g. null) and automatically substituting a default value), but few situations where it would cause problems, except that it might be a bit confusing to reassign a parameter in the middle of the method.

Do you use such warnings? Why / why not?

Note:

Avoiding this warning is of course equivalent to making the method parameter final (only then it's a compiler error :-)). So this question Why should I use the keyword "final" on a method parameter in Java? might be related.

Answer 1

The confusing-part is the reason for the warning. If you reassign a parameter a new value in the method (probably conditional), then it is not clear, what a is. That's why it is seen as good style, to leave method-params unchanged.