* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect.testing;

import com.google.common.annotations.GwtCompatible;

/**
 * A type which will never be used as the element type of any collection in our tests, and so can be

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static java.lang.Math.log;

import com.google.common.annotations.GwtIncompatible;
import java.util.Map;
import org.jspecify.annotations.NullUnmarked;

@GwtIncompatible
@NullUnmarked

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static java.lang.Math.log;

import com.google.common.annotations.GwtIncompatible;
import java.util.Set;
import org.jspecify.annotations.NullUnmarked;

@GwtIncompatible
@NullUnmarked

            return inputs.stream().map(InputSource::toString).collect(Collectors.joining(", ", "merged[", "]"));
        }
        return getModelId() + " " + getLocation();
    }

    public static InputSource merge(InputSource src1, InputSource src2) {
        return new InputSource(Stream.concat(src1.sources(), src2.sources()).collect(Collectors.toSet()));
    }

 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.CollectPreconditions.checkNonnegative;
import static com.google.common.collect.CollectPreconditions.checkRemove;
import static java.util.Objects.requireNonNull;

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import java.util.Arrays;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.collect.ReflectionFreeAssertThrows.assertThrows;

import com.google.common.annotations.GwtCompatible;
import java.util.Map;
import org.jspecify.annotations.NonNull;

import com.google.common.base.Optional;
import com.google.common.base.Predicate;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Iterables;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.reflect.ClassPath;
import com.google.common.testing.NullPointerTester.Visibility;

                .filter(StringUtil::isNotBlank)
                .distinct()
                .collect(Collectors.joining("\n")));
        body.virtualHosts = stream(entity.getVirtualHosts())
                .get(stream -> stream.filter(StringUtil::isNotBlank).distinct().map(String::trim).collect(Collectors.joining("\n")));
        return body;
    }

The user of your API (an external developer) will create an invoice in your API with a POST request.

Then your API will (let's imagine):

* Send the invoice to some customer of the external developer.
* Collect the money.
* Send a notification back to the API user (the external developer).
    * This will be done by sending a POST request (from *your API*) to some *external API* provided by that external developer (this is the "callback").