import com.google.common.collect.Iterators;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.MapDifference;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multimaps;
import com.google.common.collect.Multiset;
import com.google.common.collect.Ordering;
import com.google.common.collect.PeekingIterator;
import com.google.common.collect.Range;

import com.google.common.collect.LinkedHashMultimap;
import com.google.common.collect.LinkedHashMultiset;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multiset;
import com.google.common.collect.Ordering;
import com.google.common.collect.Range;
import com.google.common.collect.RowSortedTable;
import com.google.common.collect.SetMultimap;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import com.google.common.reflect.ClassPath;
import com.google.common.testing.NullPointerTester.Visibility;
import com.google.j2objc.annotations.J2ObjCIncompatible;

Guava is a set of core Java libraries from Google that includes new collection
types (such as multimap and multiset), immutable collections, a graph library,
and utilities for concurrency, I/O, hashing, primitives, strings, and more! It
is widely used on most Java projects within Google, and widely used by many

import com.google.common.collect.ImmutableSortedSet;
import com.google.common.collect.ImmutableTable;
import com.google.common.collect.ListMultimap;
import com.google.common.collect.MapDifference;
import com.google.common.collect.Multimap;
import com.google.common.collect.Multiset;
import com.google.common.collect.PeekingIterator;
import com.google.common.collect.Range;
import com.google.common.collect.RowSortedTable;

import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.collect.Sets;
import com.google.common.reflect.ClassPath;
import com.google.common.testing.NullPointerTester.Visibility;
import com.google.j2objc.annotations.J2ObjCIncompatible;

Typically HTTP headers work like a `Map<String, String>`: each field has one value or none. But some headers permit multiple values, like Guava's [Multimap](https://guava.dev/releases/23.0/api/docs/com/google/common/collect/Multimap.html). For example, it's legal and common for an HTTP response to supply multiple `Vary` headers. OkHttp's APIs attempt to make both cases comfortable.

    val names: Set<String> = headers.names()
    val values: List<String> = headers.values("")
    val byteCount: Long = headers.byteCount()
    val builder: Headers.Builder = headers.newBuilder()
    val multimap: Map<String, List<String>> = headers.toMultimap()
  }

  @Test
  fun headersBuilder() {
    var builder: Headers.Builder = Headers.Builder()
    builder = builder.add("")
    builder = builder.add("", "")

  // cached so that this.multimapView().inverse() only computes inverse once
  @LazyInit @CheckForNull private transient ImmutableSetMultimap<K, V> multimapView;

  /**
   * Returns a multimap view of the map.
   *
   * @since 14.0
   */
  public ImmutableSetMultimap<K, V> asMultimap() {
    if (isEmpty()) {
      return ImmutableSetMultimap.of();
    }

  // cached so that this.multimapView().inverse() only computes inverse once
  @LazyInit @CheckForNull private transient ImmutableSetMultimap<K, V> multimapView;

  /**
   * Returns a multimap view of the map.
   *
   * @since 14.0
   */
  public ImmutableSetMultimap<K, V> asMultimap() {
    if (isEmpty()) {
      return ImmutableSetMultimap.of();
    }