Several of these are explored in the next chapters of the tutorial.

## Order matters

When creating *path operations*, you can find situations where you have a fixed path.

Like `/users/me`, let's say that it's to get data about the current user.

And then you can also have a path `/users/{user_id}` to get data about a specific user by some user ID.

But it's possible to customize it, you can set a specific CDN, or serve the files yourself.

## Custom CDN for JavaScript and CSS

Let's say that you want to use a different <abbr title="Content Delivery Network">CDN</abbr>, for example you want to use `https://unpkg.com/`.

This could be useful if for example you live in a country that restricts some URLs.

 * presented below:
 *
 * <pre>
 * void runManyThings({@literal List<ThingToRun>} thingsToRun) {
 *   for (ThingToRun thingToRun : thingsToRun) {
 *     thingToRun.run(); // say this may throw an exception, but you want to
 *                       // always run all thingsToRun
 *   }
 * }
 * </pre>
 *
 * <p>This is what the code would become:
 *
 * <pre>

 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
 * or method references instead of classes, leaving your code easier to migrate in the future.
 *
 * <p>To use an existing function (say, named {@code function}) in a context where the <i>other
 * type</i> of function is expected, use the method reference {@code function::apply}. A future

    writer.write(',');
    writer.write(0xBEEF0020); // only lower 16 bits are important
    writer.write("Wo");
    writer.write("Whirled".toCharArray(), 3, 2);
    writer.write("Mad! Mad, I say", 2, 2);

    assertEquals("Hello, World!", builder.toString());
  }

  public void testAppendMethods() throws IOException {
    StringBuilder builder = new StringBuilder();

   * It's unclear whether nulls were to be permitted or forbidden, but presumably the eventual fix
   * will be to permit them, as it seems more likely that code would depend on that behavior than on
   * the other. Thus, we say the bug is in add(), which fails to support null.
   */
  @J2ktIncompatible
  @GwtIncompatible // reflection
  public static Method getAddNullSupportedMethod() {

     * because we know that newClassMap() is implemented using ConstrainedMap which is itself
     * well-tested. A purist would object to this, but what can I say, we're dirty cheaters.
     */
    map.put(Integer.class, new Integer(5));
    assertThrows(ClassCastException.class, () -> map.put(Double.class, new Long(42)));
    // Won't compile: map.put(String.class, "x");
  }

     * because we know that newClassMap() is implemented using ConstrainedMap which is itself
     * well-tested. A purist would object to this, but what can I say, we're dirty cheaters.
     */
    map.put(Integer.class, new Integer(5));
    assertThrows(ClassCastException.class, () -> map.put(Double.class, new Long(42)));
    // Won't compile: map.put(String.class, "x");
  }

   * however, {@code asMap().get(Object)} returns {@code null} instead of an empty collection.
   *
   * <p>Though the method signature doesn't say so explicitly, the returned map has {@link
   * SortedSet} values.
   */
  @Override
  public Map<K, Collection<V>> asMap() {
    return super.asMap();
  }

  /**
   * {@inheritDoc}
   *

   * however, {@code asMap().get(Object)} returns {@code null} instead of an empty collection.
   *
   * <p>Though the method signature doesn't say so explicitly, the returned map has {@link
   * SortedSet} values.
   */
  @Override
  public Map<K, Collection<V>> asMap() {
    return super.asMap();
  }

  /**
   * {@inheritDoc}
   *