{"id":2264,"date":"2025-03-03T23:05:46","date_gmt":"2025-03-03T15:05:46","guid":{"rendered":"https:\/\/www.laixuexila.com\/?p=2264"},"modified":"2025-03-03T23:05:46","modified_gmt":"2025-03-03T15:05:46","slug":"java-%e6%b3%9b%e5%9e%8b%ef%bc%88generics%ef%bc%89","status":"publish","type":"post","link":"https:\/\/www.laixuexila.com\/index.php\/2025\/03\/03\/java-%e6%b3%9b%e5%9e%8b%ef%bc%88generics%ef%bc%89\/","title":{"rendered":"Java \u6cdb\u578b\uff08Generics\uff09"},"content":{"rendered":"\n

Java \u6cdb\u578b\uff08Generics\uff09\u662f Java SE 5 \u5f15\u5165\u7684\u4e00\u4e2a\u7279\u6027\uff0c\u5b83\u5141\u8bb8\u5728 \u7c7b\u3001\u63a5\u53e3\u548c\u65b9\u6cd5<\/strong> \u4e2d\u4f7f\u7528 \u7c7b\u578b\u53c2\u6570<\/strong>\uff0c\u4ee5\u63d0\u4f9b\u66f4\u9ad8\u7684\u7c7b\u578b\u5b89\u5168\u6027\u548c\u4ee3\u7801\u590d\u7528\u6027\u3002<\/p>\n\n\n\n

\n\n\n\n

1. \u4e3a\u4ec0\u4e48\u9700\u8981\u6cdb\u578b\uff1f<\/h2>\n\n\n\n

\u5728 Java 1.5 \u4e4b\u524d\uff0c\u4f7f\u7528\u96c6\u5408\uff08\u5982 ArrayList<\/code>\uff09\u65f6\uff0c\u5b58\u50a8\u7684\u662f Object<\/code> \u7c7b\u578b\uff0c\u9700\u8981\u624b\u52a8\u8fdb\u884c\u7c7b\u578b\u8f6c\u6362\uff1a<\/p>\n\n\n\n

import java.util.ArrayList;\n\npublic class Test {\n    public static void main(String[] args) {\n        ArrayList list = new ArrayList();\n        list.add(\"Hello\");\n        list.add(123);  \/\/ \u4e0d\u5b89\u5168\n\n        String str = (String) list.get(0); \/\/ \u9700\u8981\u5f3a\u5236\u8f6c\u6362\n        System.out.println(str);\n    }\n}<\/code><\/pre>\n\n\n\n
\u7f3a\u70b9\uff1a<\/strong><\/p>\n\n\n\n
    \n
  1. \u7c7b\u578b\u4e0d\u5b89\u5168<\/strong>\uff08\u53ef\u4ee5\u5411 ArrayList<\/code> \u6dfb\u52a0\u4efb\u610f\u7c7b\u578b\u7684\u5bf9\u8c61\uff09\u3002<\/li>\n\n\n\n
  2. \u9700\u8981\u7c7b\u578b\u8f6c\u6362<\/strong>\uff0c\u5bb9\u6613\u5bfc\u81f4 ClassCastException<\/code>\u3002<\/li>\n<\/ol>\n\n\n\n
    \u89e3\u51b3\u65b9\u6848\uff1a\u4f7f\u7528\u6cdb\u578b<\/strong><\/p>\n\n\n\n
    import java.util.ArrayList;\n\npublic class Test {\n    public static void main(String[] args) {\n        ArrayList<String> list = new ArrayList<>();\n        list.add(\"Hello\");\n        \/\/ list.add(123); \/\/ \u7f16\u8bd1\u9519\u8bef\n\n        String str = list.get(0); \/\/ \u4e0d\u9700\u8981\u5f3a\u5236\u8f6c\u6362\n        System.out.println(str);\n    }\n}<\/code><\/pre>\n\n\n\n
    \n\n\n\n
    2. \u6cdb\u578b\u7684\u57fa\u672c\u4f7f\u7528<\/h2>\n\n\n\n
    2.1 \u6cdb\u578b\u7c7b<\/h3>\n\n\n\n
    \u6cdb\u578b\u7c7b\u5728\u5b9a\u4e49\u65f6\u6307\u5b9a\u4e00\u4e2a\u6216\u591a\u4e2a\u7c7b\u578b\u53c2\u6570\uff1a<\/p>\n\n\n\n
    \/\/ T \u4ee3\u8868\u4e00\u4e2a\u7c7b\u578b\u53c2\u6570\nclass Box<T> {\n    private T value;\n\n    public void setValue(T value) {\n        this.value = value;\n    }\n\n    public T getValue() {\n        return value;\n    }\n}\n\npublic class Test {\n    public static void main(String[] args) {\n        Box<String> stringBox = new Box<>();\n        stringBox.setValue(\"Hello\");\n        System.out.println(stringBox.getValue());\n\n        Box<Integer> intBox = new Box<>();\n        intBox.setValue(100);\n        System.out.println(intBox.getValue());\n    }\n}<\/code><\/pre>\n\n\n\n
    \u603b\u7ed3\uff1a<\/strong><\/p>\n\n\n\n
      \n
    • T<\/code> \u4ee3\u8868\u6cdb\u578b\u7c7b\u578b\uff0c\u53ef\u4ee5\u66ff\u6362\u4e3a\u4efb\u4f55\u5f15\u7528\u7c7b\u578b\u3002<\/li>\n\n\n\n
    • \u5728\u5b9e\u4f8b\u5316\u5bf9\u8c61\u65f6<\/strong>\uff0c\u6307\u5b9a\u5177\u4f53\u7684\u7c7b\u578b\uff0c\u5982 Box<String><\/code>\u3002<\/li>\n<\/ul>\n\n\n\n
      \n\n\n\n
      2.2 \u6cdb\u578b\u65b9\u6cd5<\/h3>\n\n\n\n
      \u6cdb\u578b\u65b9\u6cd5\u53ef\u4ee5\u5b9a\u4e49\u5728\u666e\u901a\u7c7b\u6216\u6cdb\u578b\u7c7b\u4e2d\uff1a<\/p>\n\n\n\n
      class Util {\n    \/\/ \u6cdb\u578b\u65b9\u6cd5\n    public static <T> void print(T data) {\n        System.out.println(data);\n    }\n}\n\npublic class Test {\n    public static void main(String[] args) {\n        Util.print(\"Hello\");  \/\/ \u81ea\u52a8\u63a8\u65ad T \u4e3a String\n        Util.print(100);      \/\/ \u81ea\u52a8\u63a8\u65ad T \u4e3a Integer\n        Util.print(3.14);     \/\/ \u81ea\u52a8\u63a8\u65ad T \u4e3a Double\n    }\n}<\/code><\/pre>\n\n\n\n
      \u603b\u7ed3\uff1a<\/strong><\/p>\n\n\n\n
        \n
      • \u6cdb\u578b\u65b9\u6cd5\u5728\u8fd4\u56de\u7c7b\u578b\u524d\u58f0\u660e <T><\/code> \u3002<\/li>\n\n\n\n
      • Java \u81ea\u52a8\u63a8\u65ad<\/strong> \u7c7b\u578b\uff0c\u65e0\u9700\u624b\u52a8\u6307\u5b9a\u3002<\/li>\n<\/ul>\n\n\n\n
        \n\n\n\n
        2.3 \u6cdb\u578b\u63a5\u53e3<\/h3>\n\n\n\n
        \u6cdb\u578b\u63a5\u53e3\u5141\u8bb8\u6307\u5b9a\u7c7b\u578b\uff1a<\/p>\n\n\n\n
        \/\/ \u5b9a\u4e49\u4e00\u4e2a\u6cdb\u578b\u63a5\u53e3\ninterface Container<T> {\n    void add(T item);\n    T get();\n}\n\n\/\/ \u5b9e\u73b0\u6cdb\u578b\u63a5\u53e3\uff08\u6307\u5b9a\u5177\u4f53\u7c7b\u578b\uff09\nclass StringContainer implements Container<String> {\n    private String item;\n\n    public void add(String item) {\n        this.item = item;\n    }\n\n    public String get() {\n        return item;\n    }\n}\n\n\/\/ \u5b9e\u73b0\u6cdb\u578b\u63a5\u53e3\uff08\u4fdd\u7559\u6cdb\u578b\uff09\nclass GenericContainer<T> implements Container<T> {\n    private T item;\n\n    public void add(T item) {\n        this.item = item;\n    }\n\n    public T get() {\n        return item;\n    }\n}\n\npublic class Test {\n    public static void main(String[] args) {\n        StringContainer sc = new StringContainer();\n        sc.add(\"Hello\");\n        System.out.println(sc.get());\n\n        GenericContainer<Integer> gc = new GenericContainer<>();\n        gc.add(100);\n        System.out.println(gc.get());\n    }\n}<\/code><\/pre>\n\n\n\n
        \u603b\u7ed3\uff1a<\/strong><\/p>\n\n\n\n
          \n
        • \u6cdb\u578b\u63a5\u53e3\u53ef\u4ee5\u5728\u5b9e\u73b0\u65f6\u6307\u5b9a\u5177\u4f53\u7c7b\u578b\uff0c\u4e5f\u53ef\u4ee5\u5728\u5b9e\u73b0\u7c7b\u4e2d\u7ee7\u7eed\u4f7f\u7528\u6cdb\u578b\u3002<\/li>\n<\/ul>\n\n\n\n
          \n\n\n\n
          3. \u6cdb\u578b\u7684\u7c7b\u578b\u9650\u5236\uff08\u4e0a\u754c & \u4e0b\u754c\uff09<\/h2>\n\n\n\n
          3.1 \u4e0a\u754c\u901a\u914d\u7b26 <? extends T><\/code><\/h3>\n\n\n\n
          \u7528\u4e8e\u9650\u5236\u7c7b\u578b\u5fc5\u987b\u662f T \u6216 T \u7684\u5b50\u7c7b<\/strong>\uff0c\u5e38\u7528\u4e8e \u8bfb\u53d6\u6570\u636e<\/strong> \u7684\u573a\u666f\uff1a<\/p>\n\n\n\n
          import java.util.*;\n\npublic class Test {\n    public static void printList(List<? extends Number> list) {\n        for (Number n : list) {\n            System.out.println(n);\n        }\n    }\n\n    public static void main(String[] args) {\n        List<Integer> intList = Arrays.asList(1, 2, 3);\n        List<Double> doubleList = Arrays.asList(3.14, 2.71);\n\n        printList(intList);  \/\/ OK\uff0cInteger \u662f Number \u5b50\u7c7b\n        printList(doubleList); \/\/ OK\uff0cDouble \u662f Number \u5b50\u7c7b\n    }\n}<\/code><\/pre>\n\n\n\n
          \u89c4\u5219\uff1a<\/strong><\/p>\n\n\n\n
            \n
          • ? extends Number<\/code> \u8868\u793a\u6cdb\u578b\u7c7b\u578b\u5fc5\u987b\u662f Number<\/code> \u6216\u5176\u5b50\u7c7b\u3002<\/li>\n\n\n\n
          • \u4f46\u4e0d\u80fd\u5411 list<\/code> \u6dfb\u52a0\u65b0\u5143\u7d20<\/strong>\uff0c\u56e0\u4e3a Java \u4e0d\u80fd\u786e\u5b9a\u5177\u4f53\u7684\u5b50\u7c7b\u7c7b\u578b\u3002<\/li>\n<\/ul>\n\n\n\n
            \n\n\n\n
            3.2 \u4e0b\u754c\u901a\u914d\u7b26 <? super T><\/code><\/h3>\n\n\n\n
            \u7528\u4e8e\u9650\u5236\u7c7b\u578b\u5fc5\u987b\u662f T \u6216 T \u7684\u7236\u7c7b<\/strong>\uff0c\u5e38\u7528\u4e8e \u5199\u5165\u6570\u636e<\/strong> \u7684\u573a\u666f\uff1a<\/p>\n\n\n\n
            import java.util.*;\n\npublic class Test {\n    public static void addNumbers(List<? super Integer> list) {\n        list.add(10);\n        list.add(20);\n        \/\/ list.add(3.14); \/\/ \u7f16\u8bd1\u9519\u8bef\n    }\n\n    public static void main(String[] args) {\n        List<Number> numList = new ArrayList<>();\n        addNumbers(numList); \/\/ OK\uff0cNumber \u662f Integer \u7236\u7c7b\n\n        List<Object> objList = new ArrayList<>();\n        addNumbers(objList); \/\/ OK\uff0cObject \u662f Integer \u7236\u7c7b\n    }\n}<\/code><\/pre>\n\n\n\n
            \u89c4\u5219\uff1a<\/strong><\/p>\n\n\n\n
              \n
            • ? super Integer<\/code> \u8868\u793a\u6cdb\u578b\u7c7b\u578b\u5fc5\u987b\u662f Integer<\/code> \u6216\u5176\u7236\u7c7b\uff08\u5982 Number<\/code> \u6216 Object<\/code>\uff09\u3002<\/li>\n\n\n\n
            • \u53ef\u4ee5\u5411 list<\/code> \u6dfb\u52a0 Integer<\/code> \u6216\u5176\u5b50\u7c7b\uff0c\u4f46\u4e0d\u80fd\u4fdd\u8bc1\u8bfb\u53d6\u65f6\u7684\u5177\u4f53\u7c7b\u578b<\/strong>\u3002<\/li>\n<\/ul>\n\n\n\n
              \n\n\n\n
              4. \u7c7b\u578b\u64e6\u9664\uff08Type Erasure\uff09<\/h2>\n\n\n\n
              Java \u7684\u6cdb\u578b\u662f\u7c7b\u578b\u64e6\u9664<\/strong>\u7684\uff0c\u5373\u7f16\u8bd1\u65f6\u68c0\u67e5\u7c7b\u578b\uff0c\u8fd0\u884c\u65f6\u79fb\u9664\u6cdb\u578b\u4fe1\u606f<\/strong>\u3002<\/p>\n\n\n\n
              public 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
              \u6ce8\u610f\uff1a<\/strong><\/p>\n\n\n\n
                \n
              • List<String><\/code> \u548c List<Integer><\/code> \u5728\u7f16\u8bd1\u540e\u90fd\u53d8\u6210 List<Object><\/code>\uff0c\u65e0\u6cd5\u5728\u8fd0\u884c\u65f6\u533a\u5206\u3002<\/li>\n<\/ul>\n\n\n\n
                \n\n\n\n
                5. \u4e0d\u80fd\u4f7f\u7528\u6cdb\u578b\u7684\u60c5\u51b5<\/h2>\n\n\n\n
                  \n
                • \u57fa\u672c\u6570\u636e\u7c7b\u578b\u4e0d\u80fd\u4f5c\u4e3a\u6cdb\u578b\u7c7b\u578b<\/strong>\uff08\u9700\u4f7f\u7528\u5305\u88c5\u7c7b\uff0c\u5982 int<\/code> -> Integer<\/code>\uff09\u3002<\/li>\n\n\n\n
                • \u9759\u6001\u65b9\u6cd5\u6216\u53d8\u91cf\u4e0d\u80fd\u4f7f\u7528\u7c7b\u7684\u6cdb\u578b\u53c2\u6570<\/strong>\u3002<\/li>\n\n\n\n
                • \u4e0d\u80fd\u521b\u5efa\u6cdb\u578b\u6570\u7ec4<\/strong>\uff08\u5982 T[] array = new T[10];<\/code>\uff0c\u9700\u4f7f\u7528 Object[]<\/code>\uff09\u3002<\/li>\n\n\n\n
                • \u4e0d\u80fd\u5b9e\u4f8b\u5316\u6cdb\u578b\u7c7b\u578b<\/strong>\uff08\u5982 new T();<\/code>\uff09\u3002<\/li>\n<\/ul>\n\n\n\n
                  \n\n\n\n
                  6. \u603b\u7ed3<\/h2>\n\n\n\n
                  \u6cdb\u578b\u7279\u6027<\/th>\u4f5c\u7528<\/th><\/tr><\/thead>
                  \u6cdb\u578b\u7c7b<\/td>\u5b9a\u4e49\u65f6\u4f7f\u7528\u6cdb\u578b\uff0c\u63d0\u9ad8\u4ee3\u7801\u590d\u7528\u6027<\/td><\/tr>
                  \u6cdb\u578b\u65b9\u6cd5<\/td>\u65b9\u6cd5\u7ea7\u522b\u7684\u6cdb\u578b\uff0c\u72ec\u7acb\u4e8e\u7c7b<\/td><\/tr>
                  \u6cdb\u578b\u63a5\u53e3<\/td>\u4f7f\u63a5\u53e3\u652f\u6301\u6cdb\u578b\u7c7b\u578b<\/td><\/tr>
                  \u4e0a\u754c <? extends T><\/code><\/td>\u9002\u7528\u4e8e\u8bfb\u53d6\u6570\u636e\uff0c\u4e0d\u80fd\u5199\u5165<\/td><\/tr>
                  \u4e0b\u754c <? super T><\/code><\/td>\u9002\u7528\u4e8e\u5199\u5165\u6570\u636e\uff0c\u4e0d\u80fd\u5b89\u5168\u8bfb\u53d6<\/td><\/tr>
                  \u7c7b\u578b\u64e6\u9664<\/td>\u6cdb\u578b\u4fe1\u606f\u5728\u8fd0\u884c\u65f6\u88ab\u64e6\u9664<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
                  \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":"
                  Java \u6cdb\u578b\uff08Generics\uff09\u662f Java SE 5 \u5f15\u5165\u7684\u4e00\u4e2a\u7279\u6027\uff0c\u5b83\u5141\u8bb8\u5728 \u7c7b\u3001\u63a5\u53e3\u548c\u65b9\u6cd5 \u4e2d\u4f7f\u7528 \u7c7b […]<\/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-2264","post","type-post","status-publish","format-standard","hentry","category-java"],"_links":{"self":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2264","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=2264"}],"version-history":[{"count":1,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2264\/revisions"}],"predecessor-version":[{"id":2265,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/posts\/2264\/revisions\/2265"}],"wp:attachment":[{"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/media?parent=2264"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/categories?post=2264"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laixuexila.com\/index.php\/wp-json\/wp\/v2\/tags?post=2264"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}