Java generic function: how to return Generic type

Question

Here\'s a Java generic pattern:

public  T getResultData(Class resultClass, other_args) { 
   ...
   return resultClass.cast(T-thing);
}
         


        

Answer 1

If you don't really need the exact generic type of the map and your code does not rely on that type but you're simply annoyed by the warnings you could write:

Map returnedMap;
returnedMap = thing.getResultData(Map.class, some_other_args);

then you can use any of the map methods that are not type-parametrized like containsKey, clear, iterator and so on or iterate over the entrySet or pass returnedMap to any generic method and everything will be type safe.

Map returnedMap;
returnedMap = thing.getResultData(Map.class, some_other_args);

Object myKey = ...;

Object someValue = returnedMap.get(myKey);

for (Iterator> it = returnedMap.entrySet().iterator(); it.hasNext(); )
  if (it.next().equals(myKey))
    it.remove();

for (Map.Entry e : returnedMap.entrySet()) {
  if (e.getKey().equals(myKey))
    e.setValue(null); // if the map supports null values
}

doSomething(returnedMap);

...

 void doSomething(Map map) { ... }

there is actually many things that you can do with a Map in a type-safe manner without knowing its key or value type.