* ("constant lists"). Example:
   *
   * <pre>{@code
   * public static final ImmutableList<Color> GOOGLE_COLORS
   *     = new ImmutableList.Builder<Color>()
   *         .addAll(WEBSAFE_COLORS)
   *         .add(new Color(0, 191, 255))
   *         .build();
   * }</pre>
   *
   * <p>Elements appear in the resulting list in the same order they were added to the builder.

      throw new IllegalArgumentException("key already present: " + key);
    }

    /*
     * The ordering here is important: if we deleted the key entry and then the value entry,
     * the key entry's prev or next pointer might point to the dead value entry, and when we
     * put the new entry in the key entry's position in iteration order, it might invalidate
     * the linked list.
     */

   * unchecked cast at some later point:
   *
   * <pre>
   * {@code @SuppressWarnings("unchecked") // safe because of ::isInstance check
   * ImmutableList<NewType> result =
   *     (ImmutableList) stream.filter(NewType.class::isInstance).collect(toImmutableList());}
   * </pre>
   */
  @SuppressWarnings("unchecked")
  @GwtIncompatible // Class.isInstance

   * maps ("constant maps"). Example:
   *
   * <pre>{@code
   * static final ImmutableSortedMap<Integer, String> INT_TO_WORD =
   *     new ImmutableSortedMap.Builder<Integer, String>(Ordering.natural())
   *         .put(1, "one")
   *         .put(2, "two")
   *         .put(3, "three")
   *         .buildOrThrow();
   * }</pre>
   *

   *
   * If we pick a function that goes /below/ that horizontal line, it means that we reduce the area
   * of the function, thus time. Thus, the RateLimiter becomes /faster/ after a period of
   * underutilization. If, on the other hand, we pick a function that goes /above/ that horizontal
   * line, then it means that the area (time) is increased, thus storedPermits are more costly than

    SettableFuture<String> orig = SettableFuture.create();
    SettableFuture<String> prev = orig;
    for (int i = 0; i < 100000; i++) {
      SettableFuture<String> curr = SettableFuture.create();
      prev.setFuture(curr);
      prev = curr;
    }
    // prev represents the 'innermost' future
    prev.set("done");
    assertTrue(orig.isDone());
  }

 * by factory methods has a GWT serializable type. In the following example,
 *
 * <pre>
 * {@literal @}GwtCompatible
 * class Lists {
 *   ...
 *   {@literal @}GwtCompatible(serializable = true)
 *   {@literal static <E> List<E>} newArrayList(E... elements) {
 *     ...
 *   }
 * }
 * </pre>
 *
 * <p>The return value of {@code Lists.newArrayList(E[])} has GWT serializable type. It is also

 * final WeakHashMap<Object, Object> map = new WeakHashMap<>();
 * map.put(new Object(), Boolean.TRUE);
 * GcFinalization.awaitDone(new FinalizationPredicate() {
 *   public boolean isDone() {
 *     return map.isEmpty();
 *   }
 * });
 * }</pre>
 *
 * <p>Even if your non-test code does not use finalization, you can use this class to test for
 * leaks, by ensuring that objects are no longer strongly referenced:
 *
 * <pre>{@code

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tester for equals() and hashCode() methods of a class.
 *
 * <p>The simplest use case is:
 *
 * <pre>
 * new EqualsTester().addEqualityGroup(foo).testEquals();
 * </pre>
 *
 * <p>This tests {@code foo.equals(foo)}, {@code foo.equals(null)}, and a few other operations.
 *

   * {@code Optional} class. However, this common usage:
   *
   * <pre>{@code
   * for (Foo foo : possibleFoo.asSet()) {
   *   doSomethingWith(foo);
   * }
   * }</pre>
   *
   * ... can be replaced with:
   *
   * <pre>{@code
   * possibleFoo.ifPresent(foo -> doSomethingWith(foo));
   * }</pre>
   *