ng key.
 Returns the computed value or null if no value can be computed. The
 default implementation returns null.

 <p>The method is called without synchronization: other threads may
 access the cache while this method is executing.

 <p>If a value for <code>key</code> exists in the cache when this method
 returns, the created value will be released with <code><a href="../../../reference/android/util/LruCache.html#entryRemoved(boolean, K, V, V)">entryRemoved(boolean, K, V, V)</a></code>
 and discarded. Thi