{"id":31536,"date":"2023-04-18T16:44:35","date_gmt":"2023-12-02T05:27:51","guid":{"rendered":"https:\/\/www.silicloud.com\/zh\/blog\/java%e6%b3%9b%e5%9e%8b%e7%9a%84%e6%80%bb%e7%bb%93\/"},"modified":"2024-04-30T00:07:35","modified_gmt":"2024-04-29T16:07:35","slug":"java%e6%b3%9b%e5%9e%8b%e7%9a%84%e6%80%bb%e7%bb%93","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/zh\/blog\/java%e6%b3%9b%e5%9e%8b%e7%9a%84%e6%80%bb%e7%bb%93\/","title":{"rendered":"Java\u6cdb\u578b\u7684\u603b\u7ed3"},"content":{"rendered":"<h1>\u9996\u5148<\/h1>\n<p>\u7531\u4e8e\u6700\u8fd1\u4e00\u4e9b\u65e5\u5b50\u91cd\u65b0\u7814\u7a76\u4e86Generics\uff0c\u5728\u7b80\u8981\u4ecb\u7ecdGenerics\u6982\u8981\u4e4b\u540e\uff0c\u6211\u51b3\u5b9a\u7b80\u8981\u8bb0\u5f55\u4ee5\u4e0b\u4e24\u4e2a\u5185\u5bb9\u3002<\/p>\n<ul class=\"post-ul\">\n<li style=\"list-style-type: none;\">\n<ul class=\"post-ul\">Generics\u306e\u30b9\u30b3\u30fc\u30d7<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<ul class=\"post-ul\">\u578b\u5909\u6570\u5468\u308a\u306e\u8a71\u3057<\/ul>\n<h2>\u7b80\u4ecb\uff1a\u6cdb\u578b\u6982\u5ff5\u662f\u6307\u5728\u7f16\u7a0b\u4e2d\u4f7f\u7528\u4e00\u79cd\u901a\u7528\u7684\u7c7b\u578b\u6216\u65b9\u6cd5\u6765\u5904\u7406\u591a\u79cd\u6570\u636e\u7c7b\u578b\u7684\u80fd\u529b\u3002\u5b83\u5141\u8bb8\u5728\u7f16\u8bd1\u65f6\u8fdb\u884c\u7c7b\u578b\u68c0\u67e5\u548c\u7c7b\u578b\u5b89\u5168\uff0c\u63d0\u9ad8\u4e86\u4ee3\u7801\u7684\u53ef\u91cd\u7528\u6027\u548c\u6027\u80fd\u3002\u6cdb\u578b\u4f7f\u5f97\u7a0b\u5e8f\u5458\u80fd\u591f\u7f16\u5199\u7075\u6d3b\u4e14\u53ef\u9760\u7684\u4ee3\u7801\uff0c\u540c\u65f6\u51cf\u5c11\u4e86\u4ee3\u7801\u5197\u4f59\u3002<\/h2>\n<p>\u65e0\u8bba\u5982\u4f55\uff0c\u6211\u60f3\u91cd\u65b0\u6574\u7406\u4e00\u4e0b\u4f7f\u7528Generics\u5e26\u6765\u7684\u597d\u5904\u3002\u5b83\u53ef\u4ee5\u5728\u7f16\u8bd1\u65f6\u544a\u8bc9\u6211\u4eec\u5f53\u8bd5\u56fe\u63d2\u5165\u9519\u8bef\u7684\u7c7b\u578b\u5bf9\u8c61\u65f6\uff08\u5f15\u7528\u81ea\u300aEffective Java \u7b2c3\u7248\u300b\u7b2c5\u7ae0 Generics\uff09\uff0c\u8fd9\u6837\u6211\u4eec\u5c31\u53ef\u4ee5\u5728\u4e00\u5b9a\u7a0b\u5ea6\u4e0a\u786e\u4fdd\u7c7b\u578b\u5b89\u5168\uff0c\u5e76\u5728\u5404\u79cd\u4e0d\u540c\u7c7b\u578b\u4e0a\u5b9e\u73b0\u76f8\u540c\u7684\u5904\u7406\u903b\u8f91\u3002<br \/>\n\u73b0\u5728\uff0c\u6211\u60f3\u901a\u8fc7\u4ee3\u7801\u7ed9\u51fa\u4e00\u4e9b\u5177\u4f53\u4f8b\u5b50\uff0c\u6765\u5c55\u793a\u4f7f\u7528Generics\u7684\u4f18\u70b9\u3002\u8fd9\u91cc\u6211\u4eec\u5c06\u6bd4\u8f83\u6570\u7ec4\u548cGenerics\uff0c\u5e76\u610f\u8bc6\u5230\u4f7f\u7528Generics\u7684\u597d\u5904\u3002<br \/>\n\u4ee5\u4e0b\u662f\u5728\u4e0d\u4f7f\u7528Generics\u7684\u60c5\u51b5\u4e0b\u5b9a\u4e49\u5217\u8868\u3001\u5411\u5217\u8868\u4e2d\u6dfb\u52a0\u5143\u7d20\u548c\u63d0\u53d6\u5143\u7d20\u7684\u793a\u4f8b\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">ArrayList<\/span> <span class=\"n\">list<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">ArrayList<\/span><span class=\"o\">();<\/span> \r\n<span class=\"n\">list<\/span><span class=\"o\">.<\/span><span class=\"na\">add<\/span><span class=\"o\">(<\/span><span class=\"s\">\"hoge\"<\/span><span class=\"o\">);<\/span> \r\n<span class=\"nc\">String<\/span> <span class=\"n\">s<\/span> <span class=\"o\">=<\/span> <span class=\"o\">(<\/span><span class=\"nc\">String<\/span><span class=\"o\">)<\/span> <span class=\"n\">list<\/span><span class=\"o\">.<\/span><span class=\"na\">get<\/span><span class=\"o\">(<\/span><span class=\"mi\">0<\/span><span class=\"o\">);<\/span>\r\n<\/code><\/pre>\n<p>\u9700\u8981\u660e\u786e\u5730\u8fdb\u884c\u7c7b\u578b\u8f6c\u6362\u4ee5\u4eceObject\u7c7b\u578b\u4e2d\u53d6\u51fa\uff0c\u5982\u679c\u6709\u9519\u8bef\uff08\u4f8b\u5982\u7528int\u8fdb\u884c\u8d4b\u503c\uff0c\u7136\u540e\u7528String\u8fdb\u884c\u53d6\u51fa\uff09\u5219\u65e0\u6cd5\u901a\u8fc7\u8fd0\u884c\u6765\u53d1\u73b0\u9519\u8bef\u3002\u2190\u8fd9\u4e2a\u975e\u5e38\u4ee4\u4eba\u6cae\u4e27\u3002<\/p>\n<p>\u4f7f\u7528\u6cdb\u578b\u7684\u5217\u8868\u7684\u5b9a\u4e49\uff0c\u6dfb\u52a0\u5143\u7d20\u5230\u5217\u8868\u4e2d\uff0c\u4ee5\u53ca\u4ece\u5217\u8868\u4e2d\u53d6\u51fa\u5143\u7d20\u7684\u4ee3\u7801\u5982\u4e0b\u6240\u793a\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">ArrayList<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">String<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">list<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">ArrayList<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">String<\/span><span class=\"o\">&gt;();<\/span> \r\n<span class=\"n\">list<\/span><span class=\"o\">.<\/span><span class=\"na\">add<\/span><span class=\"o\">(<\/span><span class=\"s\">\"hoge\"<\/span><span class=\"o\">);<\/span> \r\n<span class=\"nc\">String<\/span> <span class=\"n\">s<\/span> <span class=\"o\">=<\/span> <span class=\"n\">list<\/span><span class=\"o\">.<\/span><span class=\"na\">get<\/span><span class=\"o\">(<\/span><span class=\"mi\">0<\/span><span class=\"o\">);<\/span>\r\n<\/code><\/pre>\n<p>\u5728\u7f16\u8bd1\u65f6\u51fa\u73b0\u9519\u8bef\u3002\uff08\u5728\u6267\u884c\u524d\u7684\u9636\u6bb5\u5c31\u80fd\u591f\u5bdf\u89c9\u5230\u9519\u8bef\uff0c\u8fd9\u771f\u662f\u4ee4\u4eba\u9ad8\u5174\u3002\uff09<\/p>\n<h3>\u5173\u4e8e\u6cdb\u578b\u7684\u8303\u56f4<\/h3>\n<p>\u6cdb\u578b\u6709\u4e24\u4e2a\u4f5c\u7528\u57df\uff0c\u5206\u522b\u662f\u65b9\u6cd5\u4f5c\u7528\u57df\u548c\u5b9e\u4f8b\u4f5c\u7528\u57df\u3002\u4e0b\u9762\u5206\u522b\u7ed9\u51fa\u6982\u8ff0\u3002<\/p>\n<h4>\u65b9\u6cd5\u8303\u56f4<\/h4>\n<p>\u9996\u5148\uff0c\u4ee5\u4e0b\u662f\u8bed\u6cd5\u7ed3\u6784\u7684\u793a\u4f8b\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"kd\">public<\/span> <span class=\"kd\">class<\/span> <span class=\"nc\">SetInt<\/span><span class=\"o\">{<\/span>\r\n  <span class=\"kd\">public<\/span> <span class=\"o\">&lt;<\/span><span class=\"no\">E<\/span><span class=\"o\">&gt;<\/span> <span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"no\">E<\/span><span class=\"o\">&gt;<\/span> <span class=\"nf\">union<\/span><span class=\"o\">(<\/span><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"no\">E<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">s1<\/span><span class=\"o\">,<\/span><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"no\">E<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">s2<\/span><span class=\"o\">){<\/span>\r\n    <span class=\"c1\">\/\/ (\u4f8b)s1\u3068s2\u3092\u305f\u3059\u51e6\u7406<\/span>\r\n <span class=\"o\">}<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u9996\u5148\u6ce8\u610f\u5230\u7684\u662fpublic\u8bbf\u95ee\u4fee\u9970\u7b26\u540e\u9762\u7684\uff0c\u5b83\u662f\u4e00\u4e2a\u7c7b\u578b\u53d8\u91cf\u58f0\u660e\u3002\u901a\u8fc7\u8fd9\u4e2a\u58f0\u660e\uff0c\u53ef\u4ee5\u5728\u8be5\u65b9\u6cd5\u8303\u56f4\u5185\u5b9a\u4e49\u53c2\u6570\u548c\u8fd4\u56de\u503c\u5177\u6709\u76f8\u540c\u7c7b\u578b\u7684\u5bf9\u5e94\u5173\u7cfb\u3002\u5728\u65b9\u6cd5\u4f5c\u7528\u57df\u5185\uff0c\u6cdb\u578b\u58f0\u660e\u53ef\u4ee5\u7528\u4e8e\u5b9e\u4f8b\u65b9\u6cd5\uff0c\u5f53\u7136\u4e5f\u53ef\u4ee5\u7528\u4e8e\u9759\u6001\u65b9\u6cd5\u548c\u6784\u9020\u51fd\u6570\u3002<br \/>\n\u5728\u8c03\u7528\u65f6\uff0c\u53ef\u4ee5\u76f4\u63a5\u8c03\u7528\u6216\u8005\u660e\u786e\u6307\u5b9a\u7c7b\u578b\u540e\u518d\u8c03\u7528\u3002<\/p>\n<h5>\u5982\u679c\u76f4\u63a5\u8c03\u7528\u7684\u8bdd<\/h5>\n<pre class=\"post-pre\"><code><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">result<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">SetInt<\/span><span class=\"o\">.<\/span><span class=\"na\">union<\/span><span class=\"o\">(<\/span><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;,<\/span><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;);<\/span>\r\n<\/code><\/pre>\n<h5>\u5982\u679c\u9700\u8981\u660e\u786e\u6307\u5b9a\u7c7b\u578b\u5e76\u8c03\u7528\u65f6<\/h5>\n<pre class=\"post-pre\"><code><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">result<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">SetInt<\/span><span class=\"o\">.&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;<\/span><span class=\"n\">union<\/span><span class=\"o\">(<\/span><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;,<\/span><span class=\"nc\">Set<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Integer<\/span><span class=\"o\">&gt;);<\/span>\r\n<\/code><\/pre>\n<p>\u6b64\u5916\uff0c\u8fd8\u53ef\u4ee5\u901a\u8fc7\u660e\u786e\u6307\u5b9a\u7c7b\u578b\u6765\u533a\u5206\u8c03\u7528\u5f02\u5e38\u5904\u7406\u7684\u65b9\u5f0f\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"kd\">public<\/span> <span class=\"kd\">class<\/span> <span class=\"nc\">Hoge<\/span><span class=\"o\">{<\/span>\r\n    <span class=\"kd\">public<\/span> <span class=\"o\">&lt;<\/span><span class=\"no\">E<\/span> <span class=\"kd\">extends<\/span> <span class=\"nc\">Exception<\/span><span class=\"o\">&gt;<\/span> <span class=\"kt\">void<\/span> <span class=\"nf\">example<\/span><span class=\"o\">()<\/span> <span class=\"kd\">throws<\/span> <span class=\"no\">E<\/span> <span class=\"o\">{};<\/span>\r\n    <span class=\"kd\">public<\/span>  <span class=\"kt\">void<\/span> <span class=\"nf\">test<\/span><span class=\"o\">()<\/span> <span class=\"o\">{<\/span>\r\n        <span class=\"k\">try<\/span> <span class=\"o\">{<\/span>\r\n            <span class=\"k\">this<\/span><span class=\"o\">.&lt;<\/span><span class=\"nc\">IOException<\/span><span class=\"o\">&gt;<\/span><span class=\"n\">example<\/span><span class=\"o\">();<\/span>\r\n        <span class=\"o\">}<\/span> <span class=\"k\">catch<\/span> <span class=\"o\">(<\/span><span class=\"nc\">IOException<\/span> <span class=\"n\">e<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n            <span class=\"c1\">\/\/ IOException\u4f8b\u5916catch\u6642\u306e\u4f8b\u5916\u51e6\u7406<\/span>\r\n        <span class=\"o\">}<\/span>\r\n        <span class=\"k\">try<\/span> <span class=\"o\">{<\/span>\r\n            <span class=\"k\">this<\/span><span class=\"o\">.&lt;<\/span><span class=\"nc\">SQLException<\/span><span class=\"o\">&gt;<\/span><span class=\"n\">example<\/span><span class=\"o\">();<\/span>\r\n        <span class=\"o\">}<\/span> <span class=\"k\">catch<\/span> <span class=\"o\">(<\/span><span class=\"nc\">SQLException<\/span> <span class=\"n\">e<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n            <span class=\"c1\">\/\/ SQLException\u4f8b\u5916catch\u6642\u306e\u4f8b\u5916\u51e6\u7406<\/span>\r\n        <span class=\"o\">}<\/span>\r\n    <span class=\"o\">}<\/span>   \r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<h4>\u5b9e\u4f8b\u8303\u56f4<\/h4>\n<p>\u4e0e\u65b9\u6cd5\u4f5c\u7528\u57df\u76f8\u6bd4\uff0c\u5b83\u5728\u5b9e\u9645\u4f7f\u7528\u4e2d\u66f4\u5e38\u89c1\uff0c\u5e76\u4e14\u5728\u5165\u95e8\u4e66\u7c4d\u4e2d\u4e5f\u901a\u5e38\u88ab\u6d89\u53ca\u3002\u4ee5\u4e0b\u662f\u4e00\u4e2a\u4f8b\u5b50\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"kd\">public<\/span> <span class=\"kd\">class<\/span> <span class=\"nc\">Stack<\/span><span class=\"o\">&lt;<\/span><span class=\"no\">E<\/span><span class=\"o\">&gt;<\/span> <span class=\"o\">{<\/span>\r\n  <span class=\"kd\">private<\/span> <span class=\"no\">E<\/span> <span class=\"n\">elements<\/span><span class=\"o\">;<\/span>\r\n  <span class=\"kd\">public<\/span> <span class=\"kt\">void<\/span> <span class=\"nf\">push<\/span><span class=\"o\">(<\/span><span class=\"no\">E<\/span> <span class=\"n\">e<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"c1\">\/\/ elements\u306bpush\u3059\u308b\u51e6\u7406<\/span>\r\n  <span class=\"o\">}<\/span>\r\n  <span class=\"kd\">public<\/span> <span class=\"no\">E<\/span> <span class=\"nf\">pop<\/span><span class=\"o\">()<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"c1\">\/\/ elements\u304b\u3089E\u3092\u53d6\u308a\u51fa\u3059\u51e6\u7406<\/span>\r\n  <span class=\"o\">}<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u6211\u4eec\u53ef\u4ee5\u5b9a\u4e49\u591a\u4e2a\u5df2\u58f0\u660e\u7684\u5b9e\u4f8b\u65b9\u6cd5\uff08\u5982\u4e0a\u6240\u8ff0\u7684\u4e24\u4e2a\uff09\u5177\u6709\u76f8\u540c\u7684\u53c2\u6570\u3001\u8fd4\u56de\u503c\u548c\u5b9e\u4f8b\u5b57\u6bb5\u7c7b\u578b\u7684\u5bf9\u5e94\u5173\u7cfb\u3002<\/p>\n<h3>\u6709\u5173\u6cdb\u578b\u53d8\u91cf\u7684\u8ba8\u8bba<\/h3>\n<p>\u5047\u8bbe\u4f60\u5177\u5907\u5173\u4e8e&#8221;\u5171\u53d8\u3001\u9006\u53d8\u3001\u4e0d\u53d8&#8221;\u4ee5\u53ca&#8221;\u91cc\u65af\u79d1\u592b\u66ff\u6362\u539f\u5219&#8221;\u7684\u77e5\u8bc6\u3002\u5173\u4e8e\u524d\u8005\uff0c\u4f60\u53ef\u4ee5\u53c2\u8003\u8fd9\u7bc7\u6587\u7ae0\u6765\u7406\u89e3(https:\/\/www.thekingsmuseum.info\/entry\/2016\/02\/07\/235454)\u3002<br \/>\n\u5728\u4e0b\u9762\u7684\u5907\u5fd8\u5f55\u4e2d\uff0c\u6211\u4eec\u5c06\u4ee5A\u3001B\u548cC\u4e09\u4e2a\u7c7b\u4f5c\u4e3a\u4f8b\u5b50\u8fdb\u884c\u9a8c\u8bc1\uff0c\u5047\u8bbe\u5b83\u4eec\u4e4b\u95f4\u5b58\u5728\u7ee7\u627f\u5173\u7cfb\uff1aC\u7ee7\u627fB\uff0cB\u7ee7\u627fA\u3002<\/p>\n<h4>\u534f\u53d8<\/h4>\n<p>\u53ef\u4ee5\u5c06\u5176\u5b9a\u4e49\u4e3a\u5982\u4e0b\uff1a<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">List<\/span><span class=\"o\">&lt;?<\/span> <span class=\"kd\">extends<\/span> <span class=\"no\">B<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">extendsBList<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">ArrayList<\/span><span class=\"o\">&lt;<\/span><span class=\"no\">C<\/span><span class=\"o\">&gt;();<\/span>\r\n<\/code><\/pre>\n<p>\u4e0a\u8ff0\u7684extendsAList\u5177\u6709\u4ee5\u4e0b\u7279\u6027\u3002<\/p>\n<ol>\n<li style=\"list-style-type: none;\">\n<ol>\u53ef\u4ee5\u4eceextendsBList\u4e2d\u63d0\u53d6\u51faB\u578b\u548cC\u578b\u7684\u53d8\u91cf\u3002<\/ol>\n<\/li>\n<\/ol>\n<p>&nbsp;<\/p>\n<ol>extendsBList\u4e0d\u80fd\u5b58\u50a8\u9664null\u7c7b\u578b\u4ee5\u5916\u7684\u6570\u636e\u3002<\/ol>\n<p>\u5c3d\u7ba1\u6027\u8d281\u6682\u4e14\u4e0d\u8bba\uff0c\u4f46\u5bf9\u4e8e\u6027\u8d282\u4ecd\u7136\u5b58\u5728\u7591\u95ee\u3002\u4ee5\u4e0b\u662f\u5bf9\u6027\u8d282\u7684\u63a8\u5bfc\u8fc7\u7a0b\u7684\u603b\u7ed3\u3002<\/p>\n<h5>\u4e3a\u4ec0\u4e48extendsBList\u4e0d\u80fd\u5b58\u50a8\u9664\u4e86null\u7c7b\u578b\u4ee5\u5916\u7684\u5143\u7d20\uff1f<\/h5>\n<p>\u5047\u8bbe\u6211\u4eec\u53ef\u4ee5\u5c06\u65b0\u7684\u5bf9\u8c61B\u5b58\u50a8\u5728extendsBList\u4e2d\u5e76\u6267\u884cextendsBList.add\uff08new B\uff08\uff09\uff09\u3002\u4f46\u662f\u8bf7\u518d\u6b21\u53c2\u8003 extendsBList\u7684\u521d\u59cb\u5316\u4ee3\u7801\u3002\u5b83\u662f\u7528ArrayList\u7c7b\u578b\u8fdb\u884c\u521d\u59cb\u5316\u7684\u3002\u5982\u679c\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528add()\u65b9\u6cd5\u6dfb\u52a0B\u7c7b\u578b\u7684\u5bf9\u8c61\uff0c\u5219\u4f1a\u5411ArrayList\u7c7b\u578b\u4e2d\u6dfb\u52a0B\u7c7b\u578b\u7684\u5bf9\u8c61\uff0c\u8fd9\u5c06\u5bfc\u81f4\u77db\u76fe\u3002\u56e0\u6b64\uff0c\u4e3a\u4e86\u4fdd\u6301List&lt;? extends B&gt;\u7684\u7c7b\u578b\u5b89\u5168\uff0c\u53ea\u80fd\u6dfb\u52a0\u5230\u53ef\u5206\u914d\u7ed9List&lt;? extends B&gt;\u7684List<b>\u548cList\u4e2d\u7684\u5bf9\u8c61\u3002\u8fd9\u662f\u56e0\u4e3a\u53ea\u6709null\u7c7b\u578b\u624d\u6ee1\u8db3\u5c5e\u60272\u3002<\/b><\/p>\n<h4>\u53cd\u8b8a &#8211;<\/h4>\n<p>\u53ef\u4ee5\u5c06\u5176\u5b9a\u4e49\u5982\u4e0b\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">List<\/span><span class=\"o\">&lt;?<\/span> <span class=\"kd\">super<\/span> <span class=\"no\">B<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">superBList<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">ArrayList<\/span><span class=\"o\">&lt;<\/span><span class=\"no\">A<\/span><span class=\"o\">&gt;();<\/span>\r\n<\/code><\/pre>\n<p>\u4e0a\u8ff0\u7684superBList\u5177\u6709\u4ee5\u4e0b\u7279\u6027\uff1a<br \/>\n1. superBList\u80fd\u591f\u5b58\u50a8B\u578b\u548cA\u578b\u7684\u53d8\u91cf\u3002<br \/>\n2. \u4ecesuperBList\u4e2d\u53d6\u51fa\u7684\u7c7b\u578b\u662fObject\u578b\u3002<\/p>\n<p>\u6027\u8d282\u4ecd\u7136\u5b58\u5728\u7591\u95ee\u3002\u4f46\u662f\u5982\u679c\u6027\u8d281\u6210\u7acb\uff0c\u90a3\u4e48\u901a\u8fc7get()\u53d6\u51fa\u7684\u5bf9\u8c61\u53ef\u80fd\u662f\u6bd4B\u7c7b\u578b\u66f4\u9ad8\u7ea7\u7684\u5bf9\u8c61\u7c7b\u578b\u3002\u56e0\u6b64\uff0c\u5f53\u4f7f\u7528&lt;? super B&gt;\u65f6\uff0c\u53ea\u80fd\u63a5\u6536\u5230\u4f4d\u4e8e\u6240\u6709\u7c7b\u578b\u9876\u7aef\u7684Object\u7c7b\u578b\u7684get()\u8fd4\u56de\u5bf9\u8c61\u3002\u8fd9\u610f\u5473\u7740\u65e0\u6cd5\u786e\u5b9a\u8fd4\u56de\u7684\u7c7b\u578b\u4ee5\u63a5\u53d7\u5b58\u50a8\uff0c\u4e5f\u5c31\u662f\u65e0\u6cd5\u786e\u5b9a\u5c06\u8981\u8fd4\u56de\u7684\u7c7b\u578b\u3002<\/p>\n<h4>\u5173\u4e8ePECS\u539f\u5219\u3002<\/h4>\n<p>\u5728\u300aEffective Java\u300b\u7b2c\u4e8c\u7248\u7684\u7b2c28\u9879\u4e2d\uff0c\u63d0\u5230\u4e86PECS\uff08Producer Extends Consumer Super\uff09\u539f\u5219\u3002\u4ee5\u4e0b\u662f\u5f15\u6587\u3002<\/p>\n<blockquote><p>\u5982\u679c\u5728\u51fd\u6570\u5185\u90e8\uff0c\u6cdb\u578b\u53c2\u6570\u7684\u89d2\u8272\u662f&#8221;\u751f\u4ea7\u8005\uff08Producer\uff09&#8221;\uff0c\u6211\u4eec\u4f7f\u7528&#8221;extends&#8221;\uff1b\u5982\u679c\u662f&#8221;\u6d88\u8d39\u8005\uff08Consumer\uff09&#8221;\uff0c\u6211\u4eec\u4f7f\u7528&#8221;super&#8221;\u3002\u751f\u4ea7\u8005\u5728\u51fd\u6570\u5185\u90e8\u4ea7\u751f\uff08\u63d0\u4f9b\uff09\u67d0\u4e9b\u503c\u7684\u53c2\u6570\u3002\u800c\u6d88\u8d39\u8005\u5728\u51fd\u6570\u5185\u90e8\u6d88\u8d39\uff08\u5229\u7528\uff09\u67d0\u4e9b\u503c\u7684\u53c2\u6570\u3002\u8fd9\u4e2a\u539f\u5219\u901a\u5e38\u88ab\u79f0\u4e3a&#8221;PECS&#8221;\uff0c\u5373Producer-Extends and Consumer-Super\u3002<\/p><\/blockquote>\n<p>\u5982\u679c\u6839\u636e\u534f\u53d8\u548c\u9006\u53d8\u7684\u8ba8\u8bba\uff0c\u6211\u4eec\u53ef\u4ee5\u7406\u89e3\u4e3a\u4ec0\u4e48\u8981\u8fd9\u6837\u505a\u3002\u4ee5Hoge\u7c7b\u4e3a\u4f8b\u3002<\/p>\n<ul class=\"post-ul\">\n<li style=\"list-style-type: none;\">\n<ul class=\"post-ul\">\u95a2\u6570\u5074\u304b\u3089\u3059\u308c\u3070\u5024\u3092\u751f\u6210\uff08\u63d0\u4f9b\uff09\u3059\u308b\u3053\u3068\u306f\u3001\u95a2\u6570\u3092\u4f7f\u3046\u5074\u304b\u3089\u3059\u308c\u3070\u5024\u3092\u53d6\u5f97\u3059\u308b\u3053\u3068\u3001\u3059\u306a\u308f\u3061\u5024\u3092\u53d6\u308a\u51fa\u3059\u5834\u5408\u306f&lt;? extends Hoge&gt;\u3068\u3059\u308b\u3002<\/ul>\n<\/li>\n<\/ul>\n<p>&nbsp;<\/p>\n<ul class=\"post-ul\">\u95a2\u6570\u5074\u304b\u3089\u3059\u308c\u3070\u5024\u3092\u6d88\u8cbb\uff08\u5229\u7528\uff09\u3059\u308b\u3053\u3068\u306f\u3001\u95a2\u6570\u3092\u4f7f\u3046\u5074\u304b\u3089\u3059\u308c\u3070\u5024\u3092\u8a2d\u5b9a\u3059\u308b\u3053\u3068\u3001\u3059\u306a\u308f\u3061\u5024\u3092\u683c\u7d0d\u3059\u308b\u5834\u5408\u306f&lt;? super Hoge&gt;\u3068\u3059\u308b\u3002<\/ul>\n<p>\u5728\u67d0\u4e2a\u65b9\u6cd5\u4e2d\uff0c\u5982\u679c\u5728\u8be5\u65b9\u6cd5\u7684\u53c2\u6570\u4e2d\u4f7f\u7528extends\uff0c\u5728\u8be5\u65b9\u6cd5\u7684\u8fd4\u56de\u503c\u4e2d\u4f7f\u7528super\uff0c\u5c31\u53ef\u4ee5\u66f4\u5e7f\u6cdb\u5730\u91c7\u7528\u8be5\u65b9\u6cd5\u7684\u5b9e\u73b0\u3002<\/p>\n<h1>\u6700\u540e<\/h1>\n<p>\u6211\u5e0c\u671b\u80fd\u96a8\u6642\u6aa2\u67e5\u4e26\u4fee\u6539\u6587\u7ae0\u5167\u5bb9\u3002\u800c\u4e14\uff0c\u7576\u6211\u80fd\u5920\u5beb\u6cdb\u578b\u7684\u6642\u5019\uff0c\u6211\u5e0c\u671b\u80fd\u5920\u9032\u884c\u4f7f\u7528\u6cdb\u578b\u9032\u884c\u8a2d\u8a08\u3002<\/p>\n<h1>\u8bf7\u53c2\u8003<\/h1>\n<p>(https:\/\/www.amazon.co.jp\/exec\/obidos\/ASIN\/B078H61SCH\/xray2000-22\/) \u7684\u94fe\u63a5\u662f\u4e00\u4e2a\u65e5\u672c\u4e9a\u9a6c\u900a\u4ea7\u54c1\u9875\u9762\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u9996\u5148 \u7531\u4e8e\u6700\u8fd1\u4e00\u4e9b\u65e5\u5b50\u91cd\u65b0\u7814\u7a76\u4e86Generics\uff0c\u5728\u7b80\u8981\u4ecb\u7ecdGenerics\u6982\u8981\u4e4b\u540e\uff0c\u6211\u51b3\u5b9a\u7b80\u8981\u8bb0\u5f55\u4ee5\u4e0b\u4e24\u4e2a\u5185 [&hellip;]<\/p>\n","protected":false},"author":11,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-31536","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.5 (Yoast SEO v21.5) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Java\u6cdb\u578b\u7684\u603b\u7ed3 - Blog - Silicon Cloud<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" 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