How to avoid unchecked-conversion-warning in Java, if you use legacy libraries?

Question

I like the generics-feature in java and use it often. But I have a problem, if I use libraries that aren't yet aware of generics. An example are servlets. If you use ServletRequest.getParameterMap() the result will be a raw map, but it includes only String as keys and String[] as values. So I want to assign it to a Map. But for this assignement I get an warning. How can I avoid this warning with the language, not by simply suppressing the warning with the SuppressWarnings-annotation.

Answer 1

I don't think you can. The warning will appear unless you suppress it, or filter it from your IDE's warnings list.

Answer 2

How can I avoid this warning with the language, not by simply suppressing the warning with the SuppressWarnings-annotation.

The annotation is the way to avoid the warning with the language. There is no other way.

Answer 3

As others have said the warnings cannot be avoided except by suppressing them. The issue IMHO is that either you have to litter your code with annotations that apply to small scope or ignore them globally and risk errors.

IIRC there is a proposal to generate warnings where the raw types are being returned instead of at the call.

Meanwhile, I think the best approach is to use a wrapper method so that the warnings are limited to a single place, where it is safe to ignore them:

class NoWarn {
  public static Map<String, String[]> getParameterMap(ServletRequest r) 
  {
    @SuppressWarnings("unchecked")
    Map<String, String[]> result = r.getParameterMap();
    return result;
  }
}

Answer 4

The cleanest thing you can do is to encapsulate the conversion from legacy to generic code and suppress the warning only there.

E.g. you could put a generic facade on your legacy library, though this might not always be worthwhile.

Answer 5

I had the same problem, i just turned off all generic warnings and im happy :) You could also turn off serialVersionUID warning since many people dont use serialVersionUID.

in Eclipse - Window/Perferences/Java/Compiler/Errors/Warnings and turn off all Generic types.

P.S. Many bad warnings make you ignore all the warnings and some might be usefull.