{"id":3405,"date":"2023-11-02T17:20:07","date_gmt":"2023-11-02T09:20:07","guid":{"rendered":"https:\/\/xinchewhd.com.cn\/?p=3405"},"modified":"2023-11-02T17:20:07","modified_gmt":"2023-11-02T09:20:07","slug":"%e9%9d%a2%e8%af%95%e5%ae%98%e9%97%ae%ef%bc%9alist-extends-t%e4%b8%8elist-super-t%e7%9a%84%e5%8c%ba%e5%88%ab%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/xinchewhd.com.cn\/index.php\/java\/%e9%9d%a2%e8%af%95%e5%ae%98%e9%97%ae%ef%bc%9alist-extends-t%e4%b8%8elist-super-t%e7%9a%84%e5%8c%ba%e5%88%ab%ef%bc%9f\/","title":{"rendered":"\u9762\u8bd5\u5b98\u95ee\uff1aList<? extends T>\u4e0eList<? super T>\u7684\u533a\u522b\uff1f"},"content":{"rendered":"
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<\/mp-common-profile><\/section>\n<\/section>\n
\u80d6\u864e\u548c\u670b\u53cb\u539f\u521b\u7684\u89c6\u9891\u6559\u7a0b\u6709\u5174\u8da3\u7684\u53ef\u4ee5\u770b\u770b<\/strong>\uff1a<\/strong><\/span><\/p>
<\/strong><\/span><\/p>
\uff08\u6587\u672b\u9644\u8bfe\u7a0b\u5927\u7eb2\uff09<\/strong><\/span><\/p>
<\/p>
\ud83d\udc4f2023 \u6700\u65b0\uff0cJava\u6210\u795e\u4e4b\u8def\uff0c\u67b6\u6784\u89c6\u9891\uff08\u70b9\u51fb\u67e5\u770b\uff09<\/span><\/strong><\/em><\/span><\/a><\/p>
\ud83d\ude09\u8d85\u5168\u6280\u672f\u6808\u7684Java\u5165\u95e8+\u8fdb\u9636+\u5b9e\u6218\uff01<\/strong>\uff08\u70b9\u51fb\u67e5\u770b\uff09<\/em><\/span><\/strong><\/span><\/strong><\/span><\/a><\/p><\/pre>\n
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List<? extends T>\u4e0eList<? super T>\u7684\u533a\u522b<\/strong><\/span><\/p>\n
\u8fd9\u4e2a\u95ee\u9898\uff0c\u521d\u7ea7\u5de5\u7a0b\u5e08\u5728\u505a\u9762\u8bd5\u9898\u65f6\u4f1a\u51fa\u73b0\u3002\u9ad8\u7ea7\u5de5\u7a0b\u5e08\u5f88\u5c11\u4f1a\u9047\u5230\uff0c\u4f46\u5b9e\u9645\u4e0a\uff0c\u4e0d\u5c11\u5de5\u4f5c\u4e86 5 \u5e74\u5de6\u53f3\u7684\u5de5\u7a0b\u5e08\u4e5f\u56de\u7b54\u7684\u4e0d\u662f\u5f88\u597d\u3002\u57fa\u4e8e\u6b64\uff0c\u6574\u7406\u4e86\u672c\u6587\uff0c\u5206\u4eab\u7ed9\u5927\u5bb6\uff01<\/p>\n
\u6211\u4eec\u5148\u6765\u770b\u4e00\u4e0b\u540d\u8bcd\u89e3\u91ca\uff1a<\/p>\n
1\uff09\uff1f<\/span><\/h2>\n
\uff1f\u8868\u793a\u7c7b\u578b\u901a\u914d\u7b26\uff0c\u5373\u5177\u4f53\u4f20\u4ec0\u4e48\u53c2\u6570\u7c7b\u578b\uff0c\u5728List\u5b9a\u4e49\u65f6\u4e0d\u7528\u8003\u8651\u3002<\/p>\n
2\uff09<T><\/span><\/h2>\n
\u8fd9\u91cc\u7684 <> \u8868\u793a\u6cdb\u578b\uff0cT \u8868\u793a\u6cdb\u578b\u4e2d\u88c5\u8f7d\u7684\u7c7b\u578b\u4e3aT\u7c7b\u578b\uff0c\u7b49\u5230\u9700\u8981\u7684\u65f6\u5019\uff0c\u6211\u4eec\u53ef\u4ee5\u5177\u4f53\u8fd9\u4e2a T\u3002\u6211\u4eec\u5728\u4f7f\u7528\u52a8\u6001\u6570\u7ec4\u5b9e\u73b0 ArrayList \u7684\u65f6\u5019\uff0c\u5982\u679c\u5e0c\u671b\u8fd9\u4e2a ArrayList \u4e0d\u4ec5\u4ec5\u652f\u6301\u4e00\u4e2a\u7c7b\u578b\u7684\u8bdd\uff0c\u6211\u4eec\u53ef\u4ee5\u7ed9\u8fd9\u4e2a ArrayList \u5b9a\u4e49\u6cdb\u578b\uff0c\u6cdb\u578b\u4e2d\u5b58\u653e\u7684\u662fT\u7c7b\u578b\u3002\u5728\u5b9e\u9645\u521b\u5efa\u51fa\u8fd9\u4e2a ArrayList \u5bf9\u8c61\u65f6\uff0c\u6211\u4eec\u53ef\u4ee5\u6307\u5b9a\u6cdb\u578b\u4e2d\u7684\u5177\u4f53\u7c7b\u578b\u3002<\/p>\n
3\uff09<? extends T><\/span><\/h2>\n
\u7c7b\u578b\u4e0a\u754c\uff0c\u8fd9\u91cc\u7684 ? \u53ef\u4ee5\u662f T \u7c7b\u578b\u6216\u8005 T \u7684\u5b50\u7c7b\u7c7b\u578b\u3002<\/p>\n
4\uff09<? super T><\/span><\/h2>\n
\u7c7b\u578b\u4e0b\u754c\uff0c\u8fd9\u91cc\u7684?\u53ef\u4ee5\u662fT\u7c7b\u578b\u6216\u8005T\u7684\u8d85\u7c7b\u7c7b\u578b\uff0c\u4f46\u4e0d\u4ee3\u8868\u6211\u4eec\u53ef\u4ee5\u5f80\u91cc\u9762\u6dfb\u52a0\u4efb\u610f\u8d85\u7c7b\u7c7b\u578b\u7684\u5143\u7d20\u3002<\/p>\n
\u5728List\u4e2d\u5f15\u5165\u901a\u914d\u7b26\u754c\u9650\u9650\u5236\u7684\u5047\u8bbe<\/strong><\/span><\/p>\n
\u4e0d\u7ba1\u662fList<? extends T><\/code>\u8fd8\u662fList<?superT><\/code>\uff0c\u5982\u679c\u80fd\u8bfb\u53d6\u5143\u7d20\uff0c\u90a3\u4e48\u8fd9\u4e2a\u5143\u7d20\u4e00\u5b9a\u80fd\u8f6c\u5316\u4e3a T \u7c7b\u578b\uff0c\u6ce8\u610f\u4e0d\u662f\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff0c\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u662f\u5bb9\u6613\u51fa\u73b0\u95ee\u9898\u3002<\/p>\n
\u663e\u7136List<? extends T><\/code>\u5185\u90fd\u662f T \u7684\u5b50\u7c7b\u7c7b\u578b\uff0c\u80fd\u591f\u5411\u4e0a\u8f6c\u578b\u4e3a T \u7c7b\u578b\uff0c\u56e0\u6b64\u8be5 list \u53ef\u4ee5\u8bfb\u53d6\u3002<\/p>\n
\u800cList<?superT><\/code>\u5185\u53ef\u4ee5\u662f T \u7684\u8d85\u7c7b\u7c7b\u578b\uff0cT \u7684\u8d85\u7c7b\u8f6c T \u662f\u6709\u53ef\u80fd\u51fa\u73b0\u5f02\u5e38\u7684\u3002<\/p>\n
\u90a3\u6211\u5e72\u8106\u8f6c\u5316\u6210 Object \u7c7b\u578b\u4e0d\u597d\u5417\uff0c\u6240\u6709\u7c7b\u7684\u57fa\u7c7b\u90fd\u662f Object\uff0c\u4e0d\u5c5e\u4e8e\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u3002\u54e5\u4eec\uff0c\u8f6c\u6362\u6210 Object \u4e86\uff0c\u90a3\u4f60\u8fd8\u56fe\u4e2a\u5565\uff1f\u8f6c\u6362\u4e3a Object \u7c7b\u578b\u662f\u6ca1\u6709\u610f\u4e49\u7684\u3002<\/p>\n
\u5047\u8bbeList<? extends T><\/code>\u80fd\u6dfb\u52a0\u5143\u7d20\uff0c\u90a3\u4e48\u9700\u8981\u6ee1\u8db3\u6dfb\u52a0\u7684\u4efb\u610f\u5143\u7d20\u9700\u8981\u80fd\u591f\u76f4\u63a5\u8f6c\u5316\u6210 T \u7684\u4efb\u4f55\u4e00\u4e2a\u5b50\u7c7b\uff0cT \u7684\u5b50\u7c7b A \u548c\u5b50\u7c7b B \u662f\u4e0d\u80fd\u76f8\u4e92\u8f6c\u5316\u7684\uff0c\u663e\u7136\u8be5 list \u662f\u4e0d\u80fd\u6dfb\u52a0\u5143\u7d20\u7684\u3002<\/p>\n
\u5047\u8bbeList<? superT><\/code>\u80fd\u6dfb\u52a0\u5143\u7d20\uff0c\u90a3\u4e48\u540c\u6837\u9700\u8981\u6ee1\u8db3\u6dfb\u52a0\u7684\u4efb\u610f\u5143\u7d20\u80fd\u591f\u76f4\u63a5\u8f6c\u5316\u6210 T \u7684\u4efb\u4f55\u4e00\u4e2a\u8d85\u7c7b\u3002\u6b64\u65f6\u6dfb\u52a0 T \u7684\u5b50\u7c7b\u5143\u7d20\u5c31\u80fd\u6ee1\u8db3\u8be5\u8981\u6c42\uff0c\u56e0\u4e3a T \u7684\u4efb\u610f\u5b50\u7c7b\u53ef\u4ee5\u5411\u4e0a\u8f6c\u578b\u6210 T \u7684\u4efb\u4f55\u8d85\u7c7b\u3002<\/p>\n
List<? extends T><\/strong><\/span><\/p>\n
List<? extends T><\/code>\u662f\u88ab\u8bbe\u8ba1\u7528\u6765\u8bfb\u53d6\u6570\u636e\u7684\u6cdb\u578b\uff0c\u5e76\u4e14\u53ea\u80fd\u8bfb\u53d6\u7c7b\u578b\u4e3a T \u7684\u5143\u7d20\u3002\u539f\u56e0\u5982\u4e0b\uff1a<\/p>\n
\u5143\u7d20\u662f\u53ef\u4ee5\u8fdb\u884c\u5411\u4e0a\u8f6c\u578b\u7684\uff0c\u56e0\u6b64\uff0c\u6211\u4eec\u53ef\u4ee5\u8fd9\u6837\u505a\u6765\u8bfb\u53d6\u5143\u7d20\u3002<\/p>\n
List<?extendsNumber>list=new<\/span>ArrayList<>();Numbernumber=list.get(0<\/span>);<\/code><\/pre>\n
\u53ef\u4ee5\u8bfb\u53d6\uff0c\u4f46\u4e0d\u80fd\u5199\u5165\uff0c\u6bd4\u5982\u4ee5\u4e0b\u7684\u4ee3\u7801\u5c31\u76f4\u63a5\u62a5\u9519\u3002<\/p>\n
public<\/span>class<\/span>Main<\/span>{static<\/span>class<\/span>A<\/span>{}static<\/span>class<\/span>B<\/span>extends<\/span>A<\/span>{}static<\/span>class<\/span>C<\/span>extends<\/span>A<\/span>{}public<\/span>static<\/span>void<\/span>main<\/span>(String[]args){List<?extendsA>list=new<\/span>ArrayList<>();list.add(new<\/span>A());\/\/\u7f16\u8bd1\u62a5\u9519<\/span>list.add(new<\/span>B());\/\/\u7f16\u8bd1\u62a5\u9519<\/span>list.add(new<\/span>C());\/\/\u7f16\u8bd1\u62a5\u9519<\/span>}}<\/code><\/pre>\n
A \u7684\u5b50\u7c7b B \u4e0e\u5b50\u7c7b C \u662f\u4e0d\u80fd\u76f8\u4e92\u8f6c\u6362\u7684\uff0c\u56e0\u6b64\u662f\u4e0d\u80fd\u5f80\u8be5 list \u4e2d\u6dfb\u52a0\u5143\u7d20\u3002<\/p>\n
\u867d\u7136\u4e0d\u80fd\u6dfb\u52a0\u5143\u7d20\uff0c\u4f46\u53ef\u4ee5\u5728\u521d\u59cb\u5316\u7684\u65f6\u5019\uff0c\u63a5\u53d7\u4e00\u4e2a\u5df2\u7ecf\u5b9a\u4e49\u597d\u7684 list\uff0c\u800c\u8be5 list \u5b58\u653e\u7684\u7c7b\u578b\u4e00\u5b9a\u76f8\u540c\u3002\u56e0\u6b64\uff0cList<? extends T><\/code>\u53ef\u76f4\u63a5\u63a5\u53d7\u4e00\u4e2a\u5b9a\u4e49\u597d\u7684 list\u3002<\/p>\n
public<\/span>static<\/span>List<Integer>getList<\/span>(){List<Integer>list=new<\/span>ArrayList<>();list.add(1<\/span>);return<\/span>list;}\/\/....<\/span>public<\/span>static<\/span>void<\/span>main<\/span>(String[]args){List<?extendsNumber>list=new<\/span>ArrayList<>();list=getList();}<\/strong><\/code><\/pre>\n<\/section>\n
List<? super T><\/strong><\/span><\/p>\n
List<? super T><\/code>\u662f\u88ab\u8bbe\u8ba1\u7528\u6765\u6dfb\u52a0\u6570\u636e\u7684\u6cdb\u578b\uff0c\u5e76\u4e14\u53ea\u80fd\u6dfb\u52a0 T \u7c7b\u578b\u6216\u5176\u5b50\u7c7b\u7c7b\u578b\u7684\u5143\u7d20\u3002\u9762\u8bd5\u5b9d\u5178\uff1ahttps:\/\/www.yoodb.com<\/p>\n
\u4e3a\u4ec0\u4e48\u53ea\u80fd\u662f T \u7c7b\u578b\u53ca\u5176\u5b50\u7c7b\u578b\u5143\u7d20\uff0c\u8d85\u7c7b\u7c7b\u578b\u7684\u5143\u7d20\u4e0d\u53ef\u4ee5\u5417\uff1f<\/p>\n
\u8d85\u7c7b\u7c7b\u578b\u8f6c\u5316\u4e3a T \u7c7b\u578b\uff0c\u662f\u9700\u8981\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u7684\uff0c\u662f\u5bb9\u6613\u51fa\u73b0\u5f02\u5e38\u7684\uff0c\u65e0\u6cd5\u4fdd\u969c\u7684\u3002<\/p>\n
\u800c\u4f20\u5165 T \u7c7b\u578b\u53ca\u5176\u5b50\u7c7b\u7c7b\u578b\u65f6\uff0c\u80fd\u591f\u76f4\u63a5\u8f6c\u5316\u4e3a T \u7684\u4efb\u610f\u8d85\u7c7b\u7c7b\u578b\u3002\u6bd4\u5982\uff0c\u4e0b\u9762\u7684\u4ee3\u7801\u662f\u53ef\u4ee5\u8fd0\u884c\u7684<\/p>\n
public<\/span>class<\/span>Main<\/span>{static<\/span>class<\/span>A<\/span>{}static<\/span>class<\/span>B<\/span>extends<\/span>A<\/span>{}static<\/span>class<\/span>C<\/span>extends<\/span>A<\/span>{}public<\/span>static<\/span>void<\/span>main<\/span>(String[]args){List<?super<\/span>A>list=new<\/span>ArrayList<>();list.add(new<\/span>A());list.add(new<\/span>B());list.add(new<\/span>C());}}<\/code><\/pre>\n
\u8be5 list \u4e5f\u53ef\u4ee5\u8bfb\u53d6\u5176\u4e2d\u7684\u5143\u7d20\uff0c\u4ece\u7b2c\u4e8c\u8282\u53ef\u4ee5\u5f97\u51fa\uff0c\u53ea\u80fd\u7528 Object \u63a5\u6536\uff0c\u6ca1\u591a\u5927\u610f\u4e49\u3002<\/p>\n
List<?super<\/span>Integer>list2=new<\/span>ArrayList<>();list2.add(new<\/span>Integer(1<\/span>));Objectinteger=list2.get(0<\/span>);<\/code><\/pre>\n
\u5982\u679c\u6211\u4eec\u4f7f\u7528 Object \u7c7b\u578b\u6765\u63a5\u6536\u83b7\u53d6\u5230\u7684\u5143\u7d20\uff0c\u90a3\u4e48\u5143\u7d20\u672c\u8eab\u7684\u7c7b\u578b\u5c31\u4f1a\u4e22\u5931\uff0c\u56e0\u6b64\uff0c\u6211\u4eec\u4e0d\u4f7f\u7528List<? super T><\/code>\u6765\u83b7\u53d6\u5143\u7d20\u3002<\/p>\n
\u5982\u679c\u6211\u4eec\u975e\u8981\u4f7f\u7528List<? super Integer><\/code>\u4e2d\u7684 Integer \u7c7b\u578b\u6765\u63a5\u6536\u83b7\u53d6\u5230\u7684\u5143\u7d20\uff0c\u90a3\u4e48\u5fc5\u987b\u8fdb\u884c\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\uff0c\u662f\u4f1a\u51fa\u73b0\u5f02\u5e38\u7684\uff0c\u65e0\u6cd5\u4fdd\u969c\u3002<\/p>\n
List<?super<\/span>Integer>list2=new<\/span>ArrayList<>();list2.add(new<\/span>Integer(1<\/span>));Integerinteger1=(Integer)list2.get(0<\/span>);<\/code><\/pre>\n
\u603b\u7ed3<\/strong><\/span><\/p>\n
\uff081\uff09List<? extends T><\/code>\u9002\u7528\u4e8e\u8bfb\u53d6\u6570\u636e\uff0c\u8bfb\u53d6\u51fa\u6765\u7684\u6570\u636e\u5168\u90e8\u7528T\u7c7b\u578b\u63a5\u6536\u3002\u5982\u679c\u6211\u4eec\u5f80\u6b64 list \u4e2d\u6dfb\u52a0 T \u7c7b\u578b\u4e0d\u540c\u7684\u5b50\u7c7b\u7684\u8bdd\uff0c\u5404\u79cd\u5b50\u7c7b\u65e0\u6cd5\u76f8\u4e92\u8f6c\u6362\uff0c\u56e0\u6b64\u4e0d\u80fd\u6dfb\u52a0\u5143\u7d20\uff0c\u4f46\u53ef\u63a5\u53d7\u521d\u59cb\u8d4b\u503c\u3002\u516c\u4f17 \u53f7Java\u7cbe\u9009\uff0c\u56de\u590djava\u9762\u8bd5\uff0c\u83b7\u53d6\u9762\u8bd5\u8d44\u6599\uff0c\u652f\u6301\u5728\u7ebf\u5237\u9898\u3002<\/p>\n
\uff082\uff09List<? super T><\/code>\u9002\u7528\u4e8e\u6dfb\u52a0\u5143\u7d20\uff0c\u53ea\u80fd\u6dfb\u52a0 T \u7c7b\u578b\u6216\u5176\u5b50\u7c7b\u7c7b\u578b\u3002\u56e0\u4e3a\u8fd9\u4e9b\u7c7b\u578b\u90fd\u80fd\u8f6c\u6362\u4e3aT\u7684\u4efb\u610f\u8d85\u7c7b\u7c7b\u578b\uff08\u5411\u4e0a\u8f6c\u578b\uff09\uff0c\u56e0\u6b64\u6211\u4eec\u53ef\u4ee5\u5bf9\u6b64 list \u6dfb\u52a0\u5143\u7d20\u3002\u53ea\u80fd\u7528 Object \u7c7b\u578b\u6765\u63a5\u6536\u83b7\u53d6\u5230\u7684\u5143\u7d20\uff0c\u4f46\u662f\u8fd9\u4e9b\u5143\u7d20\u539f\u672c\u7684\u7c7b\u578b\u4f1a\u4e22\u5931\u3002<\/p>\n
\u66f4\u52a0\u901a\u4fd7\u6613\u61c2\u7684\u4f8b\u5b50<\/strong><\/span><\/p>\n
\u4ec0\u4e48\uff0c\u4f60\u8fd8\u6ca1\u660e\u767d\uff1f\u90a3\u6211\u4e3e\u4e00\u4e9b\u76f4\u89c2\u7684\u4f8b\u5b50\u3002<\/p>\n
\u6ce8\u610f\uff1a\u5411\u4e0a\u8f6c\u578b\u662f\u5b89\u5168\u7684\uff0c\u5411\u4e0b\u8f6c\u578b\u662f\u4e0d\u5b89\u5168\u7684\uff0c\u9664\u975e\u4f60\u77e5\u9053 List \u4e2d\u7684\u771f\u5b9e\u7c7b\u578b\uff0c\u5426\u5219\u5411\u4e0b\u8f6c\u578b\u5c31\u4f1a\u62a5\u9519<\/code>\u3002<\/p>\n
extends<\/span><\/h2>\n
List<? extends Number> foo3<\/code>\u610f\u5473\u7740\u4e0b\u9762\u7684\u8d4b\u503c\u8bed\u53e5\u90fd\u662f\u5408\u6cd5\u7684\uff1a<\/p>\n
List<?extendsNumber>foo3=new<\/span>ArrayList<Number>();\/\/Number\"extends\"Number(inthiscontext)<\/span>List<?extendsNumber>foo3=new<\/span>ArrayList<Integer>();\/\/IntegerextendsNumber<\/span>List<?extendsNumber>foo3=new<\/span>ArrayList<Double>();\/\/DoubleextendsNumber<\/span><\/code><\/pre>\n
    \n
  1. \n
    \u8bfb\u53d6<\/section>\n<\/li>\n<\/ol>\n
    \u7ed9\u5b9a\u4e0a\u8ff0\u53ef\u80fd\u7684\u8d4b\u503c\u8bed\u53e5\uff0c\u80fd\u4fdd\u8bc1\u4f60\u4eceList foo3<\/code>\u4e2d\u53d6\u51fa\u4ec0\u4e48\u6837\u7c7b\u578b\u7684\u5bf9\u8c61\uff1f<\/p>\n