/**
     * Gets the session data associated with the specified key.
     *
     * @param key the key for which to retrieve the session data, must not be {@code null}
     * @return the session data associated with the key or {@code null} if none
     */
    @Nullable
    <T> T get(@Nonnull Key<T> key);

    /**
     * Retrieve of compute the data associated with the specified key.
     *

@Experimental
public interface ArtifactManager extends Service {

    /**
     * Returns the path of the file previously associated to this artifact
     * or {@code Optional.empty()} if no path has been associated.
     */
    @Nonnull
    Optional<Path> getPath(@Nonnull Artifact artifact);

    /**
     * Associates the given file path to the artifact.
     */
    void setPath(@Nonnull Artifact artifact, Path path);

  /**
   * Maps the specified class to the specified value. Does <i>not</i> associate this value with any
   * of the class's supertypes.
   *
   * <p>{@code putInstance(Foo.class, foo)} is equivalent to {@code
   * putInstance(TypeToken.of(Foo.class), foo)}.
   *
   * @return the value previously associated with this class (possibly {@code null}), or {@code
   *     null} if there was no previous entry.
   */

  public void testPut_nullKeySupportedPresent() {
    Entry<K, V> newEntry = entry(null, v3());
    initMapWithNullKey();
    assertEquals(
        "put(present, value) should return the associated value",
        getValueForNullKey(),
        put(newEntry));

    Entry<K, V>[] expected = createArrayWithNullKey();
    expected[getNullLocation()] = newEntry;
    expectContents(expected);
  }

   */

  /**
   * Returns the value associated with the specified key, or {@code null} if there is no such value.
   *
   * <p>Specifically, if any range in this range map contains the specified key, the value
   * associated with that range is returned.
   */
  @CheckForNull
  V get(K key);

  /**
   * Returns the range containing this key and its associated value, if such a range is present in

 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface LoadingCache<K, V> extends Cache<K, V>, Function<K, V> {

  /**
   * Returns the value associated with {@code key} in this cache, first loading that value if
   * necessary. No observable state associated with this cache is modified until loading completes.
   *
   * <p>If another call to {@link #get} or {@link #getUnchecked} is currently loading the value for

        hmac.digest(response, 0, 16);
        System.arraycopy(clientChallenge, 0, response, 16, 8);
        return response;
    }


    /**
     * Generate the Unicode MD4 hash for the password associated with these credentials.
     * 
     * @param password
     * @param challenge
     * @return the calculated response
     * @throws GeneralSecurityException
     */

public interface Cache<K, V> {

  /**
   * Returns the value associated with {@code key} in this cache, or {@code null} if there is no
   * cached value for {@code key}.
   *
   * @since 11.0
   */
  @CheckForNull
  @CanIgnoreReturnValue // TODO(b/27479612): consider removing this?
  V getIfPresent(@CompatibleWith("K") Object key);

  /**
   * Returns the value associated with {@code key} in this cache, obtaining that value from {@code

  @MapFeature.Require(SUPPORTS_REMOVE)
  @CollectionSize.Require(absent = ZERO)
  public void testRemove_present() {
    int initialSize = getMap().size();
    assertEquals("remove(present) should return the associated value", v0(), getMap().remove(k0()));
    assertEquals(
        "remove(present) should decrease a map's size by one.", initialSize - 1, getMap().size());
    expectMissing(e0());
  }

  protected CacheLoader() {}

  /**
   * Computes or retrieves the value corresponding to {@code key}.
   *
   * @param key the non-null key whose value should be loaded
   * @return the value associated with {@code key}; <b>must not be null</b>
   * @throws Exception if unable to load the result
   * @throws InterruptedException if this method is interrupted. {@code InterruptedException} is