Returns the object paired with the specified key if it's
present in the cache, otherwise must return null.
Implementations of this method must have complexity of order O(1).
Differently from peek(java.lang.Object) this method not only return whether
the object is present in the cache or not, but also
applies the implemented policy that will "refresh" the cached
object in the cache, because this cached object
was really requested.
public java.lang.Object peek(java.lang.Object key)
Returns the object paired with the specified key if it's
present in the cache, otherwise must return null.
Implementations of this method must have complexity of order O(1).
This method should not apply the implemented caching policy to the
object paired with the given key, so that a client can
query if an object is cached without "refresh" its cache status. Real
requests for the object must be done using get(java.lang.Object).