assertNotNull(target);

        java.lang.annotation.ElementType[] types = target.value();
        assertEquals(5, types.length);
    }

    // Test annotation retention policy
    @Test
    public void test_annotationRetention() {

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.collect.NullnessCasts.uncheckedCastNullableTToT;
import static java.lang.Math.max;

import com.google.common.annotations.GwtCompatible;
import com.google.j2objc.annotations.Weak;
import java.util.Comparator;
import java.util.Spliterator;
import java.util.function.Consumer;
import java.util.function.DoubleConsumer;
import java.util.function.Function;

{* ../../docs_src/response_model/tutorial003_01_py310.py hl[7:10,13:14,18] *}

這樣我們能得到工具支援，對於編輯器與 mypy 來說，這段程式碼在型別上是正確的，同時我們也能得到 FastAPI 的資料過濾。

這是怎麼運作的？來看一下。🤓

### 型別註解與工具支援 { #type-annotations-and-tooling }

先看看編輯器、mypy 與其他工具會怎麼看這件事。

`BaseUser` 有基礎欄位。然後 `UserIn` 繼承自 `BaseUser` 並新增 `password` 欄位，因此它會包含兩個模型的所有欄位。

我們把函式回傳型別註解為 `BaseUser`，但實際上回傳的是 `UserIn` 實例。

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Test case for {@link EventBus}.
 *
 * @author Cliff Biffle
 */
@NullUnmarked
public class EventBusTest extends TestCase {
  private static final String EVENT = "Hello";

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;
import junit.framework.TestCase;
import org.jspecify.annotations.NullUnmarked;

/**
 * Test case for {@link EventBus}.
 *
 * @author Cliff Biffle
 */
@NullUnmarked
public class EventBusTest extends TestCase {
  private static final String EVENT = "Hello";

The `str | None` is not used by FastAPI to determine that the value is not required, it will know it's not required because it has a default value of `= None`.

But adding the type annotations will allow your editor to give you better support and detect errors.

///

## Without Pydantic { #without-pydantic }

  <description>Maven 4 CLI component, with CLI and logging support.</description>

  <dependencies>
    <!--  Maven4 API -->
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-api-annotations</artifactId>
    </dependency>
    <dependency>
      <groupId>org.apache.maven</groupId>
      <artifactId>maven-api-core</artifactId>
    </dependency>
    <dependency>
      <groupId>org.apache.maven</groupId>

  <name>PluginDescriptor</name>
  <description><![CDATA[
    Maven 4 Plugin descriptor, stored in {@code META-INF/maven/plugin.xml} in a plugin's jar artifact.
    This descriptor is generally using the information contained in the annotations of the plugin api.
    <p>An XSD is available at <a href="https://maven.apache.org/xsd/plugin-2.0.0.xsd">https://maven.apache.org/xsd/plugin-2.0.0.xsd</a></p>
  ]]></description>
  <classes>

    fun CompilationUnit.findAllIncubating() =
        findAll(Node::class.java).filter { it.isIncubating }

    private
    val Node.isIncubating: Boolean
        get() = (this as? NodeWithAnnotations<*>)?.annotations?.any { it.nameAsString == "Incubating" } ?: false

    private
    fun CompilationUnit.toVersionIncubating(sourceFile: File, node: Node) =
        Pair(

import static com.google.common.base.Predicates.not;
import static com.google.common.testing.AbstractPackageSanityTests.Chopper.suffix;

import com.google.common.annotations.GwtIncompatible;
import com.google.common.annotations.J2ktIncompatible;
import com.google.common.annotations.VisibleForTesting;
import com.google.common.base.Predicate;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;