### Top-level application { #top-level-application }

First, create the main, top-level, **FastAPI** application, and its *path operations*:

{* ../../docs_src/sub_applications/tutorial001_py310.py hl[3, 6:8] *}

### Sub-application { #sub-application }

Then, create your sub-application, and its *path operations*.

This sub-application is just another standard FastAPI application, but this is the one that will be "mounted":

- [ ] In any other case, please file an [Apache Individual Contributor License Agreement](https://www.apache.org/licenses/icla.pdf).

import java.util.PriorityQueue;
import java.util.Queue;
import org.jspecify.annotations.Nullable;

/**
 * A double-ended priority queue, which provides constant-time access to both its least element and
 * its greatest element, as determined by the queue's specified comparator. If no comparator is
 * given at creation time, the natural order of elements is used. If no maximum size is given at

  // implementations.

  private Futures() {}

  /**
   * Creates a {@code ListenableFuture} which has its value set immediately upon construction. The
   * getters just return the value. This {@code Future} can't be canceled or timed out and its
   * {@code isDone()} method always returns {@code true}.
   */
  public static <V extends @Nullable Object> ListenableFuture<V> immediateFuture(

The history of **FastAPI** is in great part the history of its predecessors.

As said in the section [Alternatives](alternatives.md):

<blockquote markdown="1">

**FastAPI** wouldn't exist if not for the previous work of others.

There have been many tools created before that have helped inspire its creation.

  /** Maps a bucket to the "entry" of its first element. */
  private transient int[] hashTableKToV;

  /** Maps a bucket to the "entry" of its first element. */
  private transient int[] hashTableVToK;

  /** Maps an "entry" to the "entry" that follows it in its bucket. */
  private transient int[] nextInBucketKToV;

  /** Maps an "entry" to the "entry" that follows it in its bucket. */

import java.util.PriorityQueue;
import java.util.Queue;
import org.jspecify.annotations.Nullable;

/**
 * A double-ended priority queue, which provides constant-time access to both its least element and
 * its greatest element, as determined by the queue's specified comparator. If no comparator is
 * given at creation time, the natural order of elements is used. If no maximum size is given at

 * href="https://github.com/ben-manes/caffeine/wiki">Caffeine</a>. Its API is designed to make it a
 * nearly drop-in replacement. Note that it is not available for Android or GWT/J2CL and that it may
 * have <a href="https://github.com/ben-manes/caffeine/wiki/Guava">different (usually better)
 * behavior</a> when multiple threads attempt concurrent mutations. Its equivalent to {@code
 * CacheBuilder} is its <a

@NullUnmarked
@GwtIncompatible
@J2ktIncompatible
public class ListenableFutureTest extends TestCase {
  public void testNoNewApis() throws Exception {
    assertWithMessage(
            "Do not add new methods to ListenableFuture. Its API needs to continue to match the"
                + " version we released in a separate artifact com.google.guava:listenablefuture.")
        .that(ListenableFuture.class.getDeclaredMethods())
        .asList()

# Calls

The HTTP client’s job is to accept your request and produce its response. This is simple in theory but it gets tricky in practice.

## [Requests](https://square.github.io/okhttp/5.x/okhttp/okhttp3/-request/)

Each HTTP request contains a URL, a method (like `GET` or `POST`), and a list of headers. Requests may also contain a body: a data stream of a specific content type.

## [Responses](https://square.github.io/okhttp/5.x/okhttp/okhttp3/-response/)