* Returns the current sum. The returned value is NOT an atomic snapshot; invocation in
   * the absence of concurrent updates returns an accurate result, but concurrent updates that occur
   * while the sum is being calculated might not be incorporated.
   *
   * @return the sum
   */
  @Override
  public long sum() {
    long sum = base;
    Cell[] as = cells;
    if (as != null) {
      int n = as.length;

    this.canonicalForm = canonicalForm;
  }

  /**
   * Returns a {@code HostSpecifier} built from the provided {@code specifier}, which is already
   * known to be valid. If the {@code specifier} might be invalid, use {@link #from(String)}
   * instead.
   *
   * <p>The specifier must be in one of these formats:
   *
   * <ul>
   *   <li>A domain name, like {@code google.com}

The **Advanced User Guide** builds on this one, uses the same concepts, and teaches you some extra features.

But you should first read the **Tutorial - User Guide** (what you are reading right now).

		// specified in the Forwarded header. The first element will always be
		// the 'for=', which we ignore, subsequently we proceed to look for
		// 'proto=' which should precede right after `for=` if not
		// we simply ignore the values and return empty. This is in line
		// with the approach we took for returning first ip from multiple
		// params.

  }

  @Override
  public boolean contains(@Nullable Object object) {
    try {
      // This set never contains null.  We need to explicitly check here
      // because some comparator might throw NPE (e.g. the natural ordering).
      return object != null && sortedDelegate.contains(object);
    } catch (ClassCastException e) {
      return false;
    }
  }

  @Override

You would also need a file `__init__.py` as you saw in [Bigger Applications - Multiple Files](../tutorial/bigger-applications.md).

///

## Settings in a dependency { #settings-in-a-dependency }

In some occasions it might be useful to provide the settings from a dependency, instead of having a global object with `settings` that is used everywhere.

    // GWT's ConcurrentHashMap is a wrapper around HashMap, but it rejects null keys, which matches
    // the behaviour of the non-GWT implementation of newConcurrentHashSet().
    // On the other hand HashSet might be better for code size if apps aren't
    // already using Collections.newSetFromMap and ConcurrentHashMap.
    return Collections.newSetFromMap(new ConcurrentHashMap<E, Boolean>());
  }

            if (nt != -1) {
                consumer.accept(dos, nt);
            }
        }

        // Assert: consumer called exactly for the 3 known codes, with the right arguments
        ArgumentCaptor<Integer> dosCaptor = ArgumentCaptor.forClass(Integer.class);
        ArgumentCaptor<Integer> ntCaptor = ArgumentCaptor.forClass(Integer.class);

        assertNotNull(notFound);

        // Test potentially retriable errors
        SmbException sharingViolation = new SmbException(NtStatus.NT_STATUS_SHARING_VIOLATION, false);
        // Sharing violations might be retriable in some contexts
        // The implementation determines this
        assertNotNull(sharingViolation);
    }

    @Test
    @DisplayName("Should preserve stack trace information")

But first, let's check some small concepts.

## In a hurry? { #in-a-hurry }

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2 { #oauth2 }

OAuth2 is a specification that defines several ways to handle authentication and authorization.