* `dict`의 키(key)는 `str`타입이다. (각 아이템의 이름(name))
    * `dict`의 값(value)는 `float`타입이다. (각 아이템의 가격(price))

#### `Optional`

`str`과 같이 타입을 선언할 때 `Optional`을 쓸 수도 있는데, "선택적(Optional)"이기때문에 `None`도 될 수 있습니다:

```Python hl_lines="1  4"
{!../../docs_src/python_types/tutorial009.py!}
```

`Optional[str]`을 `str` 대신 쓰게 되면, 특정 값이 실제로는 `None`이 될 수도 있는데 항상 `str`이라고 가정하는 상황에서 에디터가 에러를 찾게 도와줄 수 있습니다.

#### Generic(제네릭) 타입

import org.codelibs.fess.opensearch.config.exbhv.RoleTypeBhv;
import org.codelibs.fess.opensearch.config.exentity.RoleType;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.optional.OptionalEntity;

import jakarta.annotation.Resource;

/**
 * Service class for managing role types.
 */
public class RoleTypeService {

    /**
     * Constructor.
     */

`OAuth2PasswordRequestForm` is a class dependency that declares a form body with:

* The `username`.
* The `password`.
* An optional `scope` field as a big string, composed of strings separated by spaces.
* An optional `grant_type`.

/// tip

The OAuth2 spec actually *requires* a field `grant_type` with a fixed value of `password`, but `OAuth2PasswordRequestForm` doesn't enforce it.

 */
package org.apache.maven.repository;

import javax.inject.Inject;

import java.io.File;
import java.nio.file.Path;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.maven.SimpleLookup;
import org.apache.maven.api.ProducedArtifact;
import org.apache.maven.api.services.ArtifactManager;

            throws InvalidVersionSpecificationException {
        VersionRange versionRange = VersionRange.createFromVersionSpec(version);

        return artifactFactory.createDependencyArtifact(
                GROUP_ID, id, versionRange, "jar", null, scope, inheritedScope, optional);
    }

   *     in this instance of the Java virtual machine
   */
  public Optional<Charset> charset() {
    // racy single-check idiom, this is safe because Optional is immutable.
    Optional<Charset> local = parsedCharset;
    if (local == null) {
      String value = null;
      local = Optional.absent();
      for (String currentValue : parameters.get(CHARSET_ATTRIBUTE)) {
        if (value == null) {

    }

    /**
     * Implementation method for reading an XML node from an input stream.
     *
     * @param input the input stream to read from
     * @param locationBuilder optional builder for creating input location objects
     * @return the parsed XML node
     * @throws XMLStreamException if there is an error parsing the XML
     */

import java.util.Locale;

import org.codelibs.core.lang.StringUtil;
import org.codelibs.fess.entity.SearchRequestParams;
import org.codelibs.fess.mylasta.action.FessUserBean;
import org.dbflute.optional.OptionalThing;

/**
 * Abstract base class for rank fusion searchers in the Fess search system.
 * Rank fusion searchers are responsible for executing search queries and

import org.codelibs.fess.opensearch.config.exentity.PathMapping;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.response.render.RenderData;

   */
  private int findSuffixOfType(Optional<PublicSuffixType> desiredType) {
    int partsSize = parts.size();

    for (int i = 0; i < partsSize; i++) {
      String ancestorName = DOT_JOINER.join(parts.subList(i, partsSize));

      if (i > 0
          && matchesType(
              desiredType, Optional.fromNullable(PublicSuffixPatterns.UNDER.get(ancestorName)))) {
        return i - 1;