* @since 10.0 (<a href="https://github.com/google/guava/wiki/Compatibility">mostly
 *     source-compatible</a> since 4.0)
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
/*
 * The type parameter is <T> rather than <T extends @Nullable> so that we can use T in the
 * doEquivalent and doHash methods to indicate that the parameter cannot be null.
 */
public abstract class Equivalence<T>
{
  /** Constructor for use by subclasses. */