Merge "Document that LruCache is threadsafe."

 * assume a value will always be returned, even when there's a cache miss.

 *

 * <p>By default, the cache size is measured in the number of entries. Override

 * {@link #sizeOf} to size the cache in different units. For, this cache is

 * limited to 4MiB of bitmaps:

 * {@link #sizeOf} to size the cache in different units. For example, this cache

 * is limited to 4MiB of bitmaps:

 * <pre>   {@code

 *   int cacheSize = 4 * 1024 * 1024; // 4MiB

 *   LruCache<String, Bitmap> bitmapCache = new LruCache<String, Bitmap>(cacheSize) {

 *           return value.getByteCount();

 *       }

 *   }}</pre>

 *

 * <p>This class is thread-safe. Perform multiple cache operations atomically by

 * synchronizing on the cache: <pre>   {@code

 *   synchronized (cache) {

 *     if (cache.get(key) == null) {

 *         cache.put(key, value);

 *     }

 *   }}</pre>

 */

public class LruCache<K, V> {

    private final LinkedHashMap<K, V> map;