* properties, including:
   *
   * <ul>
   *   <li>{@code java.vendor.version} (added in Java 11, listed as optional as of Java 13)
   *   <li>{@code jdk.module.*} (added in Java 9, optional)
   * </ul>
   */
  public @Nullable String value() {
    return System.getProperty(key);
  }

  /** Returns a string representation of this system property. */

 * <p>This class is tailored toward use cases in common.graph. It is *NOT* a general purpose map.
 *
 * @author James Sexton
 */
class MapIteratorCache<K, V> {
  private final Map<K, V> backingMap;

  /*
   * Per JDK: "the behavior of a map entry is undefined if the backing map has been modified after
   * the entry was returned by the iterator, except through the setValue operation on the map entry"

     * <p>
     * Note: This method no longer uses internal JDK APIs for safety and compatibility.
     * It now uses the standard String constructor.
     * </p>
     *
     * @param chars
     *            the char array
     * @return a new String, or null if the input is null
     * @deprecated This method originally used internal JDK APIs (sun.misc.SharedSecrets) for

        Long.MIN_VALUE,
        Long.MAX_VALUE
      };

  private static final double[] VALUES = Doubles.concat(NUMBERS, new double[] {NaN});

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

   * even worse. For now, we just suppress and move on with our lives.
   *
   * - https://github.com/jspecify/jspecify/issues/65
   *
   * - https://github.com/jspecify/jdk/commit/71d826792b8c7ef95d492c50a274deab938f2552
   */
  /*
   * TODO(cpovirk): Is the unchecked cast avoidable? Would System.arraycopy be similarly fast (if

      try {
        // 1.8, 9, 10, 11, 12 etc
        val version = jvmVersion.toInt()
        if (version >= 9) return null
      } catch (_: NumberFormatException) {
        // expected on >= JDK 9
      }

      // Find Jetty's ALPN extension for OpenJDK.
      try {
        val alpnClassName = "org.eclipse.jetty.alpn.ALPN"
        val alpnClass = Class.forName(alpnClassName, true, null)

  @GwtIncompatible // NullPointerTester
  public void testNulls() throws NoSuchMethodException {
    NullPointerTester tester = new NullPointerTester();
    // Necessary until JDK15:
    // https://bugs.openjdk.org/browse/JDK-8202469
    tester.ignore(Equivalence.class.getMethod("wrap", Object.class));

    tester.testAllPublicStaticMethods(Equivalence.class);
    tester.testAllPublicInstanceMethods(Equivalence.equals());

  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 {

  private static final int GREATEST = Integer.MAX_VALUE;

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

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

        for (Annotation a : classOrMethod.getDeclaredAnnotations()) {
          /*
           * We avoid reflecting on NullMarked because its @Target(..., MODULE) causes problems
           * under JDK 8.
           */
          if (!(a instanceof NullMarked)
              && a.annotationType().isAnnotationPresent(TesterAnnotation.class)) {
            annotations.add(a);
          }
        }