@Override
    public String toString() {
        return "LongCache{cache=" + cache + '}';
    }
This method will return the value for the specified key if it is cached,
and if not, will calculate the value using the supplied method. The
computed value may or may not be stored in the cache afterwards. This
method is guaranteed to be lock-free, and might calculate the value
instead of using the cached one to avoid blocking.

@param key      the key to retrieve the value for
@param compute  method to use to compute the value if it is not cached
@return         the cached or computed value
common-parent/collection/src/main/java/com/speedment/common/collection/LongCache.java