KeyExtractor

```
public interface KeyExtractor<K,V>
```
Extracts an immutable key for this object.
It is important for the key to not be mutable and that the key value itself is not changed in the object. If this happens any AutoIndex, or Map using this key will break.

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`K`	`getKey(V value)` Gets the immutable key for the specified value.

Interface KeyExtractor<K,V>