protected static String formatFeatureSet(Set<? extends Feature<?>> features) {
    List<String> temp = new ArrayList<>();
    for (Feature<?> feature : features) {
      Object featureAsObject = feature; // to work around bogus JDK warning
      if (featureAsObject instanceof Enum) {
        Enum<?> f = (Enum<?>) featureAsObject;
        temp.add(f.getDeclaringClass().getSimpleName() + "." + feature);
      } else {

   * typically by writing {@code (Function<Object, String> & Serializable) Object::toString}.
   *
   * <p>For more important information about the transition from Guava's {@link Function} class to
   * the JDK {@link java.util.function.Function} class, see {@link Function}.
   */
  public static Function<Object, String> toStringFunction() {
    return ToStringFunction.INSTANCE;
  }

  // enum singleton pattern

 * the rest not null -- and the test fails if no expected exception is thrown. {@code
 * NullPointerTester} uses best effort to pick non-null default values for many common JDK and Guava
 * types, and also for interfaces and public classes that have public parameter-less constructors.
 * When the non-null default value for a particular parameter type cannot be provided by {@code

   * elements will appear in the returned list in the same order they appeared in {@code elements}.
   *
   * <p><b>Performance note:</b> According to our
   * benchmarking
   * on Open JDK 7, {@link #immutableSortedCopy} generally performs better (in both time and space)
   * than this method, and this method in turn generally performs better than copying the list and
   * calling {@link Collections#sort(List)}.
   */

 * finalization to happen. However, a call to {@code System.gc()} is specified to be no more than a
 * hint, so this technique may fail at the whim of the JDK implementation, for example if a user
 * specified the JVM flag {@code -XX:+DisableExplicitGC}. But in practice, it works very well for
 * ordinary tests.
 *

      return Types.toString(type);
    }

    boolean jdkTypeDuplicatesOwnerName() {
      return true;
    }
  }

  /**
   * Per <a href="https://github.com/google/guava/issues/1635">issue 1635</a>, In JDK 1.7.0_51-b13,
   * {@link TypeVariableImpl#equals(Object)} is changed to no longer be equal to custom TypeVariable
   * implementations. As a result, we need to make sure our TypeVariable implementation respects

 *
 * <p>An instance of this class is serializable if its reference is absent or is a serializable
 * object.
 *
 * <p><b>Comparison to {@code java.util.Optional} (JDK 8 and higher):</b> A new {@code Optional}
 * class was added for Java 8. The two classes are extremely similar, but incompatible (they cannot
 * share a common supertype). <i>All</i> known differences are listed either here or with the

  private static final short GREATEST = Short.MAX_VALUE;

  private static final short[] VALUES = {LEAST, (short) -1, (short) 0, (short) 1, GREATEST};

  // We need to test that our method behaves like the JDK method.
  @SuppressWarnings("InlineMeInliner")
  public void testHashCode() {
    for (short value : VALUES) {
      assertThat(Shorts.hashCode(value)).isEqualTo(Short.hashCode(value));
    }
  }

    INSTANCE;

    @Override
    public int compare(boolean[] left, boolean[] right) {
      // do not static import Math.min due to https://bugs.openjdk.org/browse/JDK-8357219
      @SuppressWarnings("StaticImportPreferred")
      int minLength = Math.min(left.length, right.length);
      for (int i = 0; i < minLength; i++) {
        int result = Boolean.compare(left[i], right[i]);

    INSTANCE;

    @Override
    public int compare(boolean[] left, boolean[] right) {
      // do not static import Math.min due to https://bugs.openjdk.org/browse/JDK-8357219
      @SuppressWarnings("StaticImportPreferred")
      int minLength = Math.min(left.length, right.length);
      for (int i = 0; i < minLength; i++) {
        int result = Boolean.compare(left[i], right[i]);