abstract class TypeVisitor {

  private final Set<Type> visited = Sets.newHashSet();

  /**
   * Visits the given types. Null types are ignored. This allows subclasses to call {@code
   * visit(parameterizedType.getOwnerType())} safely without having to check nulls.
   */
  public final void visit(@Nullable Type... types) {
    for (Type type : types) {
      if (type == null || !visited.add(type)) {
        // null owner type, or already visited;

            return ancestorStack.pop();
          }
          return endOfData();
        }
      };
    }

    /**
     * Visits the next node from the top iterator of {@code horizon} and returns the visited node.
     * Null is returned to indicate reaching the end of the top iterator.
     *
     * <p>For example, if horizon is {@code [[a, b], [c, d], [e]]}, {@code visitNext()} will return

   */
  static BigInteger randomNonNegativeBigInteger(int numBits) {
    int digits = RANDOM_SOURCE.nextInt(numBits);
    if (digits == 0) {
      return new BigInteger(1, RANDOM_SOURCE);
    } else {
      return new BigInteger(digits, RANDOM_SOURCE).setBit(digits);
    }
  }

  /**
   * Equivalent to calling randomPositiveBigInteger(numBits) and then flipping the sign with 50%

    int nTasks = 1000;
    int nSeededEntries = 100;
    Set<String> expectedKeys = Sets.newHashSetWithExpectedSize(nTasks + nSeededEntries);
    // seed the map, so its segments have a count>0; otherwise, clear() won't visit the in-progress
    // entries
    for (int i = 0; i < nSeededEntries; i++) {
      String s = "b" + i;
      cache.getUnchecked(s);
      expectedKeys.add(s);
    }
    computationShouldWait.set(true);

   *
   * <p>Unlike {@link Long#parseLong(String)}, this method returns {@code null} instead of throwing
   * an exception if parsing fails. Additionally, this method only accepts ASCII digits, and returns
   * {@code null} if non-ASCII digits are present in the string.
   *
   * <p>Note that strings prefixed with ASCII {@code '+'} are rejected, even under JDK 7, despite
   * the change to {@link Long#parseLong(String)} for that version.

         *
         * Ideally we'd have a real eviction policy, but until we see a problem in practice, I hope
         * that this will suffice. I have not even benchmarked with different size limits.
         */
        if (validClasses.size() > 1000) {
          validClasses.clear();
        }

        validClasses.add(new WeakReference<Class<? extends Exception>>(exceptionClass));
      }
    }

      return true;
    }
    return hasCycle(network.asGraph());
  }

  /**
   * Performs a traversal of the nodes reachable from {@code node}. If we ever reach a node we've
   * already visited (following only outgoing edges and without reusing edges), we know there's a
   * cycle in the graph.
   */
  private static <N> boolean subgraphHasCycle(
      Graph<N> graph,

        map(new TypeVariableKey(vars[i]), typeArgs[i]);
      }
      visit(rawClass);
      visit(parameterizedType.getOwnerType());
    }

    @Override
    void visitTypeVariable(TypeVariable<?> t) {
      visit(t.getBounds());
    }

    @Override
    void visitWildcardType(WildcardType t) {
      visit(t.getUpperBounds());
    }

    private void map(TypeVariableKey var, Type arg) {

    try {
      multimap().putAll(k3(), Lists.newArrayList(v3(), null));
      fail();
    } catch (NullPointerException expected) {
    }

    Collection<V> values = multimap().get(k3());
    if (values.size() == 0) {
      expectUnchanged();
      // Be extra thorough in case internal state was corrupted by the expected null.
      assertEquals(Lists.newArrayList(), Lists.newArrayList(values));

    assertThat(Lists.hashCodeImpl(base)).isEqualTo(Lists.hashCodeImpl(copy));

    assertThat(Lists.hashCodeImpl(base)).isNotEqualTo(Lists.hashCodeImpl(outOfOrder));
    assertThat(Lists.hashCodeImpl(base)).isNotEqualTo(Lists.hashCodeImpl(diffValue));
    assertThat(Lists.hashCodeImpl(base)).isNotEqualTo(Lists.hashCodeImpl(diffLength));
    assertThat(Lists.hashCodeImpl(base)).isNotEqualTo(Lists.hashCodeImpl(empty));