So, what we will do next is add the code to document how that *external API* should look like to receive the callback from *your API*.

That documentation will show up in the Swagger UI at `/docs` in your API, and it will let external developers know how to build the *external API*.

This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

/// tip

 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/NewCollectionTypesExplained#table">{@code Table}</a>.
 *
 * @author Jared Levy
 * @author Louis Wasserman
 * @since 7.0
 */
@GwtCompatible
public class TreeBasedTable<R, C, V> extends StandardRowSortedTable<R, C, V> {
  private final Comparator<? super C> columnComparator;

          shift += 24;
          len += 3;
        } else {
          int codePoint = Character.codePointAt(input, i);
          if (codePoint == c) {
            // not a valid code point; let the JDK handle invalid Unicode
            return hashBytes(input.toString().getBytes(charset));
          }
          i++;
          buffer |= codePointToFourUtf8Bytes(codePoint) << shift;

              }
            })
        .start();

    // wait for the computingEntry to be created
    computationStarted.await();
    cache.invalidateAll();
    // let the computation proceed
    computingLatch.countDown();
    // don't check cache.size() until we know the get("b") call is complete
    computationComplete.await();

              }
            })
        .start();

    // wait for the computingEntry to be created
    computationStarted.await();
    cache.invalidateAll();
    // let the computation proceed
    computingLatch.countDown();
    // don't check cache.size() until we know the get("b") call is complete
    computationComplete.await();

import junit.framework.TestCase;
import junit.framework.TestSuite;
import org.jspecify.annotations.NullMarked;

/**
 * Tests for {@code EnumBiMap}.
 *
 * @author Mike Bostock
 * @author Jared Levy
 */
@J2ktIncompatible // EnumBimap
@GwtCompatible
@NullMarked
public class EnumBiMapTest extends TestCase {
  private enum Currency {
    DOLLAR,
    FRANC,
    PESO,
    POUND,
    YEN
  }

		if m[err.Error()] > 2 {
			peersLogAlwaysIf(ctx, fmt.Errorf("Following error has been printed %d times.. %w", m[err.Error()], err))
			// Reduce the count to introduce further delay in printing
			// but let it again print after the 2th attempt
			m[err.Error()]--
			m[err.Error()]--
		}
		m[err.Error()]++
	}
}()

// Cleans up tmp directory of the local disk.
func bgFormatErasureCleanupTmp(diskPath string) {

import junit.framework.TestSuite;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * Tests for {@link Collections2}.
 *
 * @author Chris Povirk
 * @author Jared Levy
 */
@GwtCompatible
@NullMarked
public class Collections2Test extends TestCase {
  @J2ktIncompatible
  @GwtIncompatible // suite
  @AndroidIncompatible // test-suite builders
  public static Test suite() {

import java.util.SortedSet;
import org.jspecify.annotations.NullMarked;

/**
 * Generators of different types of sets and derived collections from sets.
 *
 * @author Kevin Bourrillion
 * @author Jared Levy
 * @author Hayward Chan
 */
@GwtCompatible
@NullMarked
public class SetGenerators {

  public static class ImmutableSetCopyOfGenerator extends TestStringSetGenerator {
    @Override

args) {\n    if (typeof event !== 'string' || !element) {\n      return null\n    }\n\n    const $ = getjQuery()\n    const typeEvent = getTypeEvent(event)\n    const inNamespace = event !== typeEvent\n\n    let jQueryEvent = null\n    let bubbles = true\n    let nativeDispatch = true\n    let defaultPrevented = false\n\n    if (inNamespace && $) {\n      jQueryEvent = $.Event(event, args)\n\n      $(element).trigger(jQueryEvent)\n      bubbles = !jQueryEvent.isPropagationStopped()\n      nativeDispatch...