{"id":2266,"date":"2025-03-03T23:06:52","date_gmt":"2025-03-03T15:06:52","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=2266"},"modified":"2025-03-03T23:06:52","modified_gmt":"2025-03-03T15:06:52","slug":"%e6%b7%b1%e5%85%a5%e8%ae%b2%e8%a7%a3-java-%e6%b3%9b%e5%9e%8b","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/03\/03\/%e6%b7%b1%e5%85%a5%e8%ae%b2%e8%a7%a3-java-%e6%b3%9b%e5%9e%8b\/","title":{"rendered":"\u6df1\u5165\u8bb2\u89e3 Java \u6cdb\u578b"},"content":{"rendered":"\n

\u5728\u57fa\u7840\u6cdb\u578b\u7684\u4f7f\u7528\u4e0a\uff0c\u4f60\u5df2\u7ecf\u4e86\u89e3\u4e86\u6cdb\u578b\u7c7b\u3001\u6cdb\u578b\u65b9\u6cd5\u3001\u6cdb\u578b\u63a5\u53e3\u3001\u901a\u914d\u7b26\u4ee5\u53ca\u7c7b\u578b\u64e6\u9664\u7b49\u5185\u5bb9\u3002\u63a5\u4e0b\u6765\uff0c\u6211\u4eec\u5c06\u8fdb\u4e00\u6b65\u6df1\u5165\u63a2\u8ba8 Java \u6cdb\u578b\u7684\u9ad8\u7ea7\u7279\u6027\u3001\u6cdb\u578b\u5728\u53cd\u5c04\u4e2d\u7684\u5e94\u7528\u3001\u6cdb\u578b\u4e0e\u6570\u7ec4\u3001\u6cdb\u578b\u7684\u8fd0\u884c\u65f6\u884c\u4e3a\uff0c\u4ee5\u53ca\u6cdb\u578b\u5728\u6570\u636e\u5e93\u64cd\u4f5c\u548c Spring \u6846\u67b6\u4e2d\u7684\u5e94\u7528<\/strong>\u3002<\/p>\n\n\n\n

\n\n\n\n

1. \u6cdb\u578b\u7684\u9ad8\u7ea7\u7279\u6027<\/strong><\/h1>\n\n\n\n

1.1 \u6cdb\u578b\u7684\u5d4c\u5957<\/strong><\/h3>\n\n\n\n

\u6cdb\u578b\u53ef\u4ee5\u5d4c\u5957\u4f7f\u7528\uff0c\u4f8b\u5982 List<List<String>><\/code>\uff1a<\/p>\n\n\n\n

import java.util.*;\n\npublic class Test {\n    public static void main(String[] args) {\n        List<List<String>> list = new ArrayList<>();\n        List<String> innerList = new ArrayList<>();\n        innerList.add(\"Hello\");\n        list.add(innerList);\n\n        System.out.println(list.get(0).get(0)); \/\/ \u8f93\u51fa Hello\n    }\n}<\/code><\/pre>\n\n\n\n
\u5d4c\u5957\u6cdb\u578b\u5728\u5904\u7406\u590d\u6742\u6570\u636e\u7ed3\u6784\uff08\u5982 Map<String, List<Integer>><\/code>\uff09\u65f6\u975e\u5e38\u6709\u7528\u3002<\/p>\n\n\n\n
\n\n\n\n
1.2 \u6cdb\u578b\u4e0e\u7ee7\u627f<\/strong><\/h3>\n\n\n\n
\u5728 Java \u4e2d\uff0c\u6cdb\u578b\u4e0d\u80fd\u88ab\u7ee7\u627f<\/strong>\uff0c\u4f46\u53ef\u4ee5\u8fdb\u884c\u7c7b\u578b\u534f\u53d8\uff08Covariance\uff09\u4e0e\u9006\u53d8\uff08Contravariance\uff09<\/strong>\uff1a<\/p>\n\n\n\n
List<String> stringList = new ArrayList<>();\nList<Object> objectList = stringList; \/\/ \u7f16\u8bd1\u9519\u8bef\uff01<\/code><\/pre>\n\n\n\n
\u6cdb\u578b\u662f\u4e0d\u53d8\u7684\uff0cList<String><\/code> \u4e0d\u662f List<Object><\/code> \u7684\u5b50\u7c7b<\/strong>\uff0c\u9700\u8981\u4f7f\u7528 \u901a\u914d\u7b26<\/strong>\uff1a<\/p>\n\n\n\n
List<? extends Object> list = new ArrayList<String>(); \/\/ \u5141\u8bb8<\/code><\/pre>\n\n\n\n
\u6cdb\u578b\u901a\u914d\u7b26<\/th>\u4f5c\u7528<\/th><\/tr><\/thead>
<? extends T><\/code><\/td>\u9002\u7528\u4e8e \u8bfb\u53d6\u6570\u636e<\/strong>\uff0c\u4e0d\u80fd\u5199\u5165\uff08\u9664\u4e86 null<\/code>\uff09<\/td><\/tr>
<? super T><\/code><\/td>\u9002\u7528\u4e8e \u5199\u5165\u6570\u636e<\/strong>\uff0c\u53ef\u4ee5\u5b89\u5168\u5199\u5165 T<\/code> \u7c7b\u578b<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
\u793a\u4f8b\uff1a<\/p>\n\n\n\n
import java.util.*;\n\npublic class Test {\n    public static void main(String[] args) {\n        List<? extends Number> numList = new ArrayList<Integer>();\n        \/\/ numList.add(100); \/\/ \u7f16\u8bd1\u9519\u8bef\uff08\u4e0d\u80fd\u5199\u5165\uff09\n\n        List<? super Integer> intList = new ArrayList<Number>();\n        intList.add(100); \/\/ \u5141\u8bb8\u5199\u5165 Integer \u6216\u5176\u5b50\u7c7b\n    }\n}<\/code><\/pre>\n\n\n\n
\n\n\n\n
1.3 \u6cdb\u578b\u65b9\u6cd5\u7684\u591a\u91cd\u7ea6\u675f<\/strong><\/h3>\n\n\n\n
\u4f60\u53ef\u4ee5\u5bf9\u6cdb\u578b\u53c2\u6570\u6dfb\u52a0\u591a\u4e2a\u7ea6\u675f\uff1a<\/p>\n\n\n\n
\/\/ T \u5fc5\u987b\u662f Number \u7684\u5b50\u7c7b\uff0c\u5e76\u4e14\u5b9e\u73b0 Comparable \u63a5\u53e3\npublic static <T extends Number & Comparable<T>> T findMax(T a, T b) {\n    return a.compareTo(b) > 0 ? a : b;\n}\n\npublic class Test {\n    public static void main(String[] args) {\n        System.out.println(findMax(10, 20));  \/\/ \u8f93\u51fa 20\n    }\n}<\/code><\/pre>\n\n\n\n
\u6ce8\u610f\uff1a<\/strong><\/p>\n\n\n\n
    \n
  • Java \u53ea\u652f\u6301\u5355\u7ee7\u627f\uff0c\u4f46\u53ef\u4ee5\u540c\u65f6\u5b9e\u73b0\u591a\u4e2a\u63a5\u53e3<\/strong>\u3002<\/li>\n\n\n\n
  • T extends A & B<\/code> \u4e2d A \u5fc5\u987b\u662f\u7c7b\uff0cB \u5fc5\u987b\u662f\u63a5\u53e3<\/strong>\u3002<\/li>\n<\/ul>\n\n\n\n
    \n\n\n\n
    2. \u6cdb\u578b\u4e0e\u53cd\u5c04<\/strong><\/h1>\n\n\n\n
    2.1 \u8fd0\u884c\u65f6\u83b7\u53d6\u6cdb\u578b\u7c7b\u578b<\/strong><\/h3>\n\n\n\n
    \u7531\u4e8e\u7c7b\u578b\u64e6\u9664\uff08Type Erasure\uff09<\/strong>\uff0c\u5728\u8fd0\u884c\u65f6\u65e0\u6cd5\u76f4\u63a5\u83b7\u53d6\u6cdb\u578b\u7c7b\u578b\uff1a<\/p>\n\n\n\n
    import java.util.ArrayList;\nimport java.util.List;\n\npublic class Test {\n    public static void main(String[] args) {\n        List<String> list1 = new ArrayList<>();\n        List<Integer> list2 = new ArrayList<>();\n\n        System.out.println(list1.getClass() == list2.getClass()); \/\/ true\n    }\n}<\/code><\/pre>\n\n\n\n
    \u89e3\u51b3\u65b9\u6848\uff1a\u4f7f\u7528\u53cd\u5c04\u83b7\u53d6\u6cdb\u578b\u53c2\u6570<\/strong><\/p>\n\n\n\n
    import java.lang.reflect.ParameterizedType;\nimport java.lang.reflect.Type;\n\nclass GenericClass<T> {}\n\npublic class Test {\n    public static void main(String[] args) {\n        GenericClass<String> obj = new GenericClass<String>() {};\n        Type type = obj.getClass().getGenericSuperclass();\n        if (type instanceof ParameterizedType) {\n            Type[] actualTypeArgs = ((ParameterizedType) type).getActualTypeArguments();\n            System.out.println(actualTypeArgs[0]); \/\/ class java.lang.String\n        }\n    }\n}<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    2.2 \u53cd\u5c04\u521b\u5efa\u6cdb\u578b\u5b9e\u4f8b<\/strong><\/h3>\n\n\n\n
    \u5982\u679c\u6cdb\u578b\u7c7b\u4e2d\u9700\u8981\u4f7f\u7528\u53cd\u5c04\u521b\u5efa\u5bf9\u8c61\uff1a<\/p>\n\n\n\n
    class Container<T> {\n    private Class<T> type;\n\n    public Container(Class<T> type) {\n        this.type = type;\n    }\n\n    public T createInstance() throws InstantiationException, IllegalAccessException {\n        return type.newInstance();\n    }\n}\n\npublic class Test {\n    public static void main(String[] args) throws InstantiationException, IllegalAccessException {\n        Container<String> container = new Container<>(String.class);\n        String str = container.createInstance();\n        System.out.println(str);\n    }\n}<\/code><\/pre>\n\n\n\n
    \u6ce8\u610f\uff1a<\/strong><\/p>\n\n\n\n
      \n
    • newInstance()<\/code> \u9700\u8981\u65e0\u53c2\u6784\u9020\u51fd\u6570\u3002<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      3. \u6cdb\u578b\u4e0e\u6570\u7ec4<\/strong><\/h1>\n\n\n\n
      3.1 \u6cdb\u578b\u6570\u7ec4\u7684\u9650\u5236<\/strong><\/h3>\n\n\n\n
      \u5728 Java \u4e2d\uff0c\u4e0d\u80fd\u76f4\u63a5\u521b\u5efa\u6cdb\u578b\u6570\u7ec4<\/strong>\uff1a<\/p>\n\n\n\n
      T[] array = new T[10]; \/\/ \u7f16\u8bd1\u9519\u8bef<\/code><\/pre>\n\n\n\n
      \u89e3\u51b3\u65b9\u6848\uff1a<\/strong><\/p>\n\n\n\n
      @SuppressWarnings(\"unchecked\")\nT[] array = (T[]) new Object[10]; <\/code><\/pre>\n\n\n\n
      \u6216\u8005\u4f7f\u7528 Array.newInstance()<\/code>\uff1a<\/p>\n\n\n\n
      import java.lang.reflect.Array;\n\npublic class Test {\n    public static <T> T[] createArray(Class<T> clazz, int size) {\n        return (T[]) Array.newInstance(clazz, size);\n    }\n\n    public static void main(String[] args) {\n        String[] arr = createArray(String.class, 5);\n        System.out.println(arr.length); \/\/ \u8f93\u51fa 5\n    }\n}<\/code><\/pre>\n\n\n\n
      \n\n\n\n
      4. \u6cdb\u578b\u5728\u6570\u636e\u5e93\u64cd\u4f5c\u4e2d\u7684\u5e94\u7528<\/strong><\/h1>\n\n\n\n
      \u6cdb\u578b\u5728 DAO\uff08Data Access Object\uff09\u6a21\u5f0f<\/strong> \u4e2d\u88ab\u5e7f\u6cdb\u4f7f\u7528\uff1a<\/p>\n\n\n\n
      import java.util.List;\n\ninterface GenericDAO<T> {\n    void save(T entity);\n    T findById(int id);\n    List<T> findAll();\n}\n\nclass User {\n    private int id;\n    private String name;\n\n    public User(int id, String name) {\n        this.id = id;\n        this.name = name;\n    }\n\n    public String getName() {\n        return name;\n    }\n}\n\nclass UserDAO implements GenericDAO<User> {\n    @Override\n    public void save(User user) {\n        System.out.println(\"Saving user: \" + user.getName());\n    }\n\n    @Override\n    public User findById(int id) {\n        return new User(id, \"Mock User\");\n    }\n\n    @Override\n    public List<User> findAll() {\n        return List.of(new User(1, \"Alice\"), new User(2, \"Bob\"));\n    }\n}\n\npublic class Test {\n    public static void main(String[] args) {\n        UserDAO userDAO = new UserDAO();\n        userDAO.save(new User(1, \"Charlie\"));\n        User user = userDAO.findById(1);\n        System.out.println(user.getName());\n    }\n}<\/code><\/pre>\n\n\n\n
      \n\n\n\n
      5. \u6cdb\u578b\u5728 Spring \u6846\u67b6\u4e2d\u7684\u5e94\u7528<\/strong><\/h1>\n\n\n\n
      5.1 Spring \u4e2d\u7684\u6cdb\u578b\u4f9d\u8d56\u6ce8\u5165<\/strong><\/h3>\n\n\n\n
      Spring \u5141\u8bb8\u901a\u8fc7\u6cdb\u578b\u81ea\u52a8\u6ce8\u5165<\/strong>\u9002\u914d\u7684 Bean\uff1a<\/p>\n\n\n\n
      @Component\npublic class GenericService<T> {\n    public void printType(T obj) {\n        System.out.println(obj.getClass().getName());\n    }\n}\n\n@Service\npublic class UserService extends GenericService<User> {}\n\npublic class Test {\n    public static void main(String[] args) {\n        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);\n        UserService userService = context.getBean(UserService.class);\n        userService.printType(new User(1, \"Alice\")); \n    }\n}<\/code><\/pre>\n\n\n\n
      Spring \u901a\u8fc7\u6cdb\u578b\u53c2\u6570\u89e3\u6790<\/strong>\uff0c\u81ea\u52a8\u4e3a UserService<\/code> \u6ce8\u5165 User<\/code> \u7c7b\u578b\u3002<\/p>\n\n\n\n
      \n\n\n\n
      \u603b\u7ed3<\/strong><\/h1>\n\n\n\n
      \u77e5\u8bc6\u70b9<\/th>\u8bf4\u660e<\/th><\/tr><\/thead>
      \u6cdb\u578b\u7ee7\u627f<\/td>\u6cdb\u578b\u662f\u4e0d\u53d8\u7684\uff0cList<String><\/code> \u4e0d\u662f List<Object><\/code><\/td><\/tr>
      \u8fd0\u884c\u65f6\u53cd\u5c04<\/td>\u901a\u8fc7 ParameterizedType<\/code> \u83b7\u53d6\u6cdb\u578b\u53c2\u6570<\/td><\/tr>
      \u6cdb\u578b\u6570\u7ec4<\/td>\u4e0d\u80fd\u76f4\u63a5\u521b\u5efa\uff0c\u9700 Array.newInstance()<\/code><\/td><\/tr>
      \u6cdb\u578b DAO<\/td>\u6cdb\u578b\u5e94\u7528\u4e8e\u6570\u636e\u5e93\u64cd\u4f5c\uff0c\u63d0\u5347\u4ee3\u7801\u590d\u7528\u6027<\/td><\/tr>
      \u6cdb\u578b\u4e0e Spring<\/td>\u7528\u4e8e\u81ea\u52a8\u6ce8\u5165\u548c\u901a\u7528\u670d\u52a1<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
      \u66f4\u591a\u8be6\u7ec6\u5185\u5bb9\u8bf7\u5173\u6ce8\u5176\u4ed6\u76f8\u5173\u6587\u7ae0\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
      \u5728\u57fa\u7840\u6cdb\u578b\u7684\u4f7f\u7528\u4e0a\uff0c\u4f60\u5df2\u7ecf\u4e86\u89e3\u4e86\u6cdb\u578b\u7c7b\u3001\u6cdb\u578b\u65b9\u6cd5\u3001\u6cdb\u578b\u63a5\u53e3\u3001\u901a\u914d\u7b26\u4ee5\u53ca\u7c7b\u578b\u64e6\u9664\u7b49\u5185\u5bb9\u3002\u63a5\u4e0b\u6765\uff0c\u6211\u4eec\u5c06\u8fdb\u4e00\u6b65\u6df1\u5165 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[68],"tags":[],"class_list":["post-2266","post","type-post","status-publish","format-standard","hentry","category-java"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2266","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/comments?post=2266"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2266\/revisions"}],"predecessor-version":[{"id":2267,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2266\/revisions\/2267"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=2266"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=2266"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=2266"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}