{"id":852,"date":"2021-12-18T20:42:39","date_gmt":"2021-12-18T12:42:39","guid":{"rendered":"https:\/\/blog.cauchyschwarz.com\/?p=852"},"modified":"2021-12-18T20:42:43","modified_gmt":"2021-12-18T12:42:43","slug":"java-language","status":"publish","type":"post","link":"https:\/\/blog.cauchyschwarz.com\/?p=852","title":{"rendered":"Java Language"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">\u603b\u662f\u60f3\u91cd\u65b0\u5b66\u4e60\u4e00\u904dJava\uff0c\u6216\u8005\u89c9\u5f97\u81ea\u5df1\u638c\u63e1\u4e0d\u591f\u624e\u5b9e\u60f3\u8865\u5168\u4e00\u4e0b\uff0c\u9664\u4e86Oracle\u7684\u5b98\u65b9\u6559\u7a0b\u5916\uff0c\u6700\u8fd1\u53d1\u73b0\u4e86logicbig.com\u8fd9\u4e2a\u7f51\u7ad9\uff0c\u4e0a\u9762\u7684\u57fa\u672c\u90fd\u5e26\u6709\u5b8c\u6574\u7684\u4ee3\u7801\u5b9e\u4f8b\uff0c\u8bb2\u89e3\u4e5f\u6e05\u695a\u7b80\u6d01\uff0c\u6392\u7248\u4e5f\u5f88\u597d\u770b\uff0c\u6240\u4ee5\u6700\u8fd1\u5f00\u59cb\u8ba4\u771f\u843d\u5b9e\u8fd9\u4e2a\u4e00\u76f4\u4ee5\u6765\u90fd\u6709\u7684\u60f3\u6cd5\u3002Oracle\u7684\u5b98\u65b9\u6559\u7a0b\u5176\u5b9e\u4e5f\u5f88\u597d\uff0c\u5c31\u662f\u67af\u71e5\u4e86\u70b9\uff0c\u4ee3\u7801\u6ca1\u6709\u9ad8\u4eae\u663e\u793a\uff0c\u770b\u7740\u5bb9\u6613\u7761\u89c9\u3002<\/p>\n\n\n\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 ez-toc-wrap-right counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-6a28d6ebbeab1\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6a28d6ebbeab1\" checked aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=852\/#checked_vs_unchecked_exception\" >checked vs. unchecked exception<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=852\/#covariant_return_type\" >covariant return type<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=852\/#%E5%85%B3%E4%BA%8E%E6%B3%9B%E5%9E%8B%E3%80%81%E6%95%B0%E7%BB%84%E3%80%81%E6%96%B9%E6%B3%95%E8%BF%94%E5%9B%9E%E5%80%BC%E7%9A%84%E5%8D%8F%E5%8F%98%E3%80%81%E9%80%86%E5%8F%98%E3%80%81%E5%8F%8C%E5%8F%98%E5%92%8C%E4%B8%8D%E5%8F%98%E6%80%A7\" >\u5173\u4e8e\u6cdb\u578b\u3001\u6570\u7ec4\u3001\u65b9\u6cd5\u8fd4\u56de\u503c\u7684\u534f\u53d8\u3001\u9006\u53d8\u3001\u53cc\u53d8\u548c\u4e0d\u53d8\u6027<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=852\/#Java%E4%B8%AD%E6%9D%A1%E4%BB%B6%E8%BF%90%E7%AE%97%E7%AC%A6%E7%9A%84%E7%BB%93%E6%9E%9C%E7%9A%84%E7%B1%BB%E5%9E%8B%E5%88%A4%E5%AE%9A%E8%A7%84%E5%88%99\" >Java\u4e2d\u6761\u4ef6\u8fd0\u7b97\u7b26\u7684\u7ed3\u679c\u7684\u7c7b\u578b\u5224\u5b9a\u89c4\u5219<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=852\/#%E5%8F%82%E8%80%83\" >\u53c2\u8003<\/a><\/li><\/ul><\/nav><\/div>\n<h1 class=\"wp-block-heading\" id=\"checked-vs-unchecked-exception\"><span class=\"ez-toc-section\" id=\"checked_vs_unchecked_exception\"><\/span>checked vs. unchecked exception<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0b\u9762\u662fException\u7684\u7ee7\u627f\u5173\u7cfb\u56fe\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"928\" height=\"817\" src=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/ExceptionHierarchy.png\" alt=\"\" class=\"wp-image-853\" srcset=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/ExceptionHierarchy.png 928w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/ExceptionHierarchy-300x264.png 300w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/ExceptionHierarchy-768x676.png 768w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/ExceptionHierarchy-670x590.png 670w\" sizes=\"auto, (max-width: 928px) 100vw, 928px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\u9664\u4e86Error\u3001RuntimeException\u8fd9\u4e24\u4e2a\u7c7b\u4ee5\u53ca\u4ed6\u4eec\u7684\u5b50\u7c7b\uff0c\u5176\u4ed6\u7c7b\u578b\u7684Exception\u90fd\u662f\u9700\u8981\u7528catch\u5904\u7406\u7684\u3002\u5f53\u7a0b\u5e8f\u4e2d\u51fa\u73b0Error\u3001RuntimeException\u53ca\u76f8\u5e94\u5b50\u7c7b\u65f6\u4ee3\u8868jvm\u9047\u5230\u4e86\u9519\u8bef(unrecoverable\uff09\uff0c\u76f4\u63a5\u8ba9\u7a0b\u5e8f\u51fa\u9519\u9000\u51fa\u5c31\u597d\uff0c\u4e0d\u7528catch\u3002\u8fd9\u4e9bexception\u5c31\u662funchecked exception\u3002\u800c\u5bf9\u4e8e\u5176\u4ed6\u7c7b\u578b\u7684exception\uff0c\u4ed6\u4eec\u662f\u7f16\u5199\u7a0b\u5e8f\u662f\u5c31\u9884\u8ba1\u5230\u53ef\u80fd\u4f1a\u4ea7\u751f\u7684\u7a0b\u5e8f\u72b6\u6001\uff0c\u56e0\u6b64\u9700\u8981\u7a0b\u5e8f\u8fdb\u884c\u76f8\u5e94\u7684\u5904\u7406\u3002\u8fd9\u4e9bexception\u662fchecked exception\u3002<br>unchecked exception\u4e5f\u53ef\u4ee5\u50cfchecked exception\u4e00\u6837\u8fdb\u884ccatch\u5904\u7406\uff0c\u4f46\u53cd\u8fc7\u6765checked exception\u4e0d\u80fd\u50cfunchecked exception\u4e00\u6837\u4e0d\u88abcatch\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"covariant-return-type\"><span class=\"ez-toc-section\" id=\"covariant_return_type\"><\/span>covariant return type<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u5b50\u7c7b\u5728\u91cd\u8f7d\u7236\u7c7b\u7684\u65b9\u6cd5\u65f6\uff0c\u88ab\u91cd\u8f7d\u7236\u7c7b\u65b9\u6cd5\u7684\u8fd4\u56de\u503c\u7c7b\u578b\u5728\u5b50\u7c7b\u7684\u5b9e\u73b0\u4e2d\u53ef\u4ee5\u7528\u8be5\u7c7b\u578b\u7684\u5b50\u7c7b\u4ee3\u66ff\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"java\" class=\"language-java\">public class CovariantReturnExample {\n\n    interface SuperType {\n    }\n\n    interface SubType extends SuperType {\n    }\n\n    interface A {\n        SuperType getType ();\n    }\n\n    interface B extends A {\n        SubType getType ();\n    }\n}\n<\/code><\/pre>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"688\" height=\"355\" src=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/covariant-returns.png\" alt=\"\" class=\"wp-image-854\" srcset=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/covariant-returns.png 688w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/covariant-returns-300x155.png 300w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/covariant-returns-670x346.png 670w\" sizes=\"auto, (max-width: 688px) 100vw, 688px\" \/><\/figure>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"%E5%85%B3%E4%BA%8E%E6%B3%9B%E5%9E%8B%E6%95%B0%E7%BB%84%E6%96%B9%E6%B3%95%E8%BF%94%E5%9B%9E%E5%80%BC%E7%9A%84%E5%8D%8F%E5%8F%98%E9%80%86%E5%8F%98%E5%8F%8C%E5%8F%98%E5%92%8C%E4%B8%8D%E5%8F%98%E6%80%A7\"><span class=\"ez-toc-section\" id=\"%E5%85%B3%E4%BA%8E%E6%B3%9B%E5%9E%8B%E3%80%81%E6%95%B0%E7%BB%84%E3%80%81%E6%96%B9%E6%B3%95%E8%BF%94%E5%9B%9E%E5%80%BC%E7%9A%84%E5%8D%8F%E5%8F%98%E3%80%81%E9%80%86%E5%8F%98%E3%80%81%E5%8F%8C%E5%8F%98%E5%92%8C%E4%B8%8D%E5%8F%98%E6%80%A7\"><\/span>\u5173\u4e8e\u6cdb\u578b\u3001\u6570\u7ec4\u3001\u65b9\u6cd5\u8fd4\u56de\u503c\u7684\u534f\u53d8\u3001\u9006\u53d8\u3001\u53cc\u53d8\u548c\u4e0d\u53d8\u6027<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u5173\u4e8e\u6570\u7ec4\u534f\u53d8\u7684\u7406\u89e3\uff0c\u53c2\u8003<a href=\"https:\/\/stackoverflow.com\/a\/12370259\/5357784\">\u8fd9\u4e2a\u56de\u7b54<\/a>\uff1a<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\"><p><strong>\u6211\u4eec\u7ecf\u5e38\u6216\u8005Java Specificatoin\u8bf4Subtype[]\u662fSupertype[]\u7684\u5b50\u7c7b\uff0c\u4f46\u5176\u5b9e\u5e94\u8be5\u4e0d\u662f\uff01<\/strong>\u3002\u4e00\u4e2a\u81ea\u7136\u7684\u60f3\u6cd5\uff1a\u5982\u679c\u79f0\u4e00\u4e2a\u7c7b\u4e3a\u53e6\u4e00\u4e2a\u7c7b\u7684\u5b50\u7c7b\uff0c\u90a3\u4e48<strong>\u5b50\u7c7b\u5e94\u8be5\u80fd\u505a\u7236\u7c7b\u80fd\u591f\u505a\u7684\u4e8b\u60c5<\/strong>\u3002\u4f46\u662fSupertype[]\u53ef\u4ee5\u5b58\u50a8Supertype\u7c7b\u578b\u7684\u5bf9\u8c61\uff0cSubtype[]\u5374\u4e0d\u53ef\u4ee5\u3002\u6240\u4ee5\u628aSubtype[]\u5f53\u505aSupertype[]\u7684\u5b50\u7c7b\u53ef\u770b\u4f5c\u4e3aJava\u7684\u4e00\u4e2a\u7455\u75b5\uff0c\u4f5c\u4e3a\u517c\u5bb9\u6027\u88ab\u4fdd\u7559\u4e86\u4e0b\u6765\u3002\u800cJava\u5728\u540e\u9762\u5f15\u5165\u6cdb\u578b\u65f6\u5c31\u7406\u6e05\u4e86\u8fd9\u4e2a\u95ee\u9898\uff1aGeneric&lt;Supertype&gt;\u548cGeneric&lt;Subtype&gt;\u6ca1\u6709\u4efb\u4f55\u5173\u7cfb\u3002<\/p><\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">\u5173\u4e8e\u6570\u7ec4\u534f\u53d8\u8fd9\u4e2a\u7455\u75b5\u5bfc\u81f4\u7684\u95ee\u9898\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"java\" class=\"language-java\">public class CovariantArraysExample {\n\n  public static void main(String[] args) {\n      Integer[] integers = new Integer[10];\n      Number[] numbers = integers;\n      numbers[0] = new Double(25);\n  }\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u56e0\u4e3a\u628aSubtype[]\u5f53\u505aSupertype[]\u5b50\u7c7b\u8fd9\u79cd\u9519\u8bef\u7406\u89e3(\u7f16\u8bd1\u5668\u4e5f\u662f\u8fd9\u4e48\u7406\u89e3\u7684)\uff0c\u4e0a\u9762\u8fd9\u4e2a\u7a0b\u5e8f\u662f\u53ef\u4ee5\u7f16\u8bd1\u901a\u8fc7\u7684\uff0c\u6211\u4eec\u89c9\u5f97Integer[]\u8fd9\u4e2a\u5b50\u7c7b\u5c31\u662f\u53ef\u4ee5\u50cfNumber[]\u7236\u7c7b\u4e00\u6837\u5b58\u50a8\u4e00\u4e2aNumber\u5bf9\u8c61\uff0c\u4f46\u662f\u5230\u4e86\u8fd0\u884c\u65f6\u7684\u65f6\u5019\uff0cInteger[]\u51b3\u5b9a\u8981\u5b58\u50a8\u8fd9\u4e2aNumber\u5bf9\u8c61\uff0c\u7136\u540e\u53d1\u73b0\u8fd9\u4e2aNumber\u5bf9\u8c61\u5b9e\u9645\u7c7b\u578b\u4e3aDouble\uff0c\u4e0d\u7ba1\u628a\u8fd9\u4e2a\u5bf9\u8c61\u770b\u4f5c\u662fNumber\u8fd8\u662fDouble\uff0c\u90fd\u4e0d\u662fInteger[]\u80fd\u591f\u5b58\u50a8\u7684Integer\u7c7b\u578b\uff0c\u4e8e\u662f\u5c31\u53ea\u6709\u62a5ArrayStoreException\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"java\" class=\"language-java\">public class CovariantArraysExample {\n\n  public static void main(String[] args) {\n      Integer[] integers = new Integer[10];\n      Number[] numbers = integers;\n      numbers[0] = new Integer(25);\n  }\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5bf9\u4e8e\u8fd9\u4e2a\u7a0b\u5e8f\u60c5\u51b5\u7a0d\u6709\u4e0d\u540c\uff0cInteger[]\u5728\u51b3\u5b9a\u8981\u5b58\u50a8\u8fd9\u4e2aNumber\u5bf9\u8c61\u65f6\uff0c\u53d1\u73b0\u8fd9\u4e2aNumber\u5bf9\u8c61\u5b9e\u9645\u662f\u4e2a\u81ea\u5df1\u53ef\u4ee5\u5b58\u50a8\u7684Integer\uff0c\u56e0\u6b64\u5c31\u53ef\u4ee5\u6b63\u786e\u5b58\u50a8\u8be5\u5bf9\u8c61\uff0c\u4e0d\u4f1a\u62a5ArrayStoreException\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>\u4e0a\u9762\u5199\u7684\u4e24\u4e2a\u7a0b\u5e8f\u5747\u53ef\u4ee5\u901a\u8fc7\u7f16\u8bd1\uff0c\u4f46\u662f\u8fd0\u884c\u65f6\u5374\u6709\u4e00\u4e2a\u4f1a\u62a5\u9519\uff0c\u7f16\u8bd1\u5668\u5bf9\u8fd9\u79cd\u4ee3\u7801\u5199\u6cd5\u7684\u5bb9\u5fcd\u6f5c\u5728\u5730\u589e\u52a0\u4e86\u6211\u4eec\u5199\u51fabug\u4ee3\u7801\u7684\u53ef\u80fd\u6027\u3002<\/strong><\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u66f4\u597d\u7684\u6cdb\u578b<br><strong>\u5f15\u5165\u6cdb\u578b\u7684\u539f\u56e0\uff1a<\/strong>&nbsp;\u4fdd\u8bc1\u7f16\u8bd1\u65f6\u7684\u7c7b\u578b\u5b89\u5168\uff0c\u901a\u8fc7\u4f7f\u7528\u6cdb\u578b\u4e0d\u4f1a\u51fa\u73b0\u7f16\u8bd1\u901a\u8fc7\u4e86\u4f46\u5230\u4e86\u8fd0\u884c\u65f6\u5374\u53c8\u7c7b\u578b\u4e0d\u5339\u914d\u7684\u95ee\u9898\u3002<br>\u9996\u5148\uff0c\u6cdb\u578b\u660e\u786e\u4e86Generic&lt;Subtype&gt;\u548cGeneric&lt;Supertype&gt;\u662f\u4e24\u4e2a\u8def\u4eba\uff0c\u6ca1\u6709\u4efb\u4f55\u5173\u7cfb\u3002<br>\u5176\u6b21\uff0c\u6cdb\u578b\u8981\u60f3\u529e\u6cd5\u907f\u514d\u4e0a\u9762\u90a3\u79cd\u7f16\u8bd1\u8fc7\u4e86\u8fd0\u884c\u65f6\u5374\u53ef\u80fd\u51fa\u9519\u7684\u60c5\u51b5\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"java\" class=\"language-java\">public class InvariantGenericsExample {\n\n  public static void main(String[] args) {\n      List&lt;Integer&gt; integers = new ArrayList&lt;&gt;();\n      List&lt;Number&gt; numbers = new ArrayList&lt;&gt;();\n      numbers = integers;\n  }\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u7531\u4e8eList&lt;Integer&gt;\u548cList&lt;Number&gt;\u662f\u4e0d\u76f8\u5e72\u7684\u4e24\u4e2a\u7c7b\u578b\uff0c\u56e0\u6b64\u4e0a\u9762\u7684\u4ee3\u7801\u5728\u7f16\u8bd1\u65f6\u5c31\u4f1a\u51fa\u9519\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"java\" class=\"language-java\">public class CovariantGenericsExample2 {\n\n  public static void main(String[] args) {\n      List&lt;Integer&gt; integers = new ArrayList&lt;&gt;();\n      integers.add(1);\n\n      List&lt;? extends Number&gt; numbers = integers;\n      Double d = new Double(23);\n      numbers.add(d);\n  }\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u628aList&lt;Integer&gt;\u8d4b\u503c\u7ed9List&lt;? extends Number&gt;\u662f\u53ef\u53d6\u7684\uff0c\u4f46\u662f\u4e0a\u9762\u7684\u7a0b\u5e8f\u662f\u4f1a\u7f16\u8bd1\u51fa\u9519\u7684\uff0c\u56e0\u4e3aList&lt;? extends Number&gt;\u91cc\u7684\u901a\u914d\u7b26\u7c7b\u578b(?)\u662f<strong>capture<\/strong>\u7c7b\u578b\uff0c\u65e0\u8bba\u540e\u9762\u8fd9\u4e2a\u53d8\u91cf<em>d<\/em>\u662fDouble\u8fd8\u662fInteger\u7c7b\u578b\uff0c\u90fd\u662f\u548c\u8fd9\u4e2a<strong>capture<\/strong>\u7c7b\u578b\u4e0d\u76f8\u5339\u914d\u7684\uff0c\u56e0\u6b64\u4f1a\u7f16\u8bd1\u51fa\u9519\u3002\u50cf\u4e0a\u9762\u8fd9\u79cd\u8d4b\u503c\u540e\u7684numbers\u53ea\u80fd\u8bfb\u53d6\u6216\u8005\u5220\u9664\u5217\u8868\u91cc\u7684\u5185\u5bb9\uff0c\u4e0d\u80fd\u5bf9\u5176\u8fdb\u884c\u6dfb\u52a0\u6216\u8005\u4fee\u6539\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code lang=\"java\" class=\"language-java\">public class ContravariantGenericsExample {\n\n    public static void main(String[] args) {\n        List&lt;A&gt; aList = new ArrayList&lt;&gt;();\n        aList.add(new A());\n\n        List&lt;? super B&gt; bList = aList;\n        bList.add(new B());\n\n        System.out.println(bList);\n    }\n\n    private static class A {\n    }\n\n    private static class B extends A {\n    }\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0a\u9762\u7684\u7a0b\u5e8f\u5374\u53c8\u662f\u53ef\u4ee5\u6b63\u5e38\u7f16\u8bd1\u8fd0\u884c\u7684\uff0c\u56e0\u4e3aList&lt;? super B&gt;\u91cc\u7684\u8fd9\u4e2a<strong>capture<\/strong>\u7c7b\u578b\u59cb\u7ec8\u662fB\u7684\u7236\u7c7b\uff0c\u90a3\u4e48\u5411\u4e00\u4e2a\u7236\u7c7b\u7684\u5217\u8868\u91cc\u6dfb\u52a0\u4e00\u4e2a\u5b50\u7c7b\u5bf9\u8c61\u81ea\u7136\u662f\u53ef\u4ee5\u7684\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>\u5173\u4e8e\u8fd9\u4e2a\u6cdb\u578b\u3001\u534f\u53d8\u4e4b\u7c7b\u7684\u4e1c\u897f\u611f\u89c9\u81ea\u5df1\u4e5f\u8fd8\u6ca1\u6709\u641e\u6e05\u695a\uff0c\u9700\u8981\u4ee5Oracle\u5b98\u65b9\u6587\u6863\u4e3a\u51c6\u3002<\/strong><\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"java%E4%B8%AD%E6%9D%A1%E4%BB%B6%E8%BF%90%E7%AE%97%E7%AC%A6%E7%9A%84%E7%BB%93%E6%9E%9C%E7%9A%84%E7%B1%BB%E5%9E%8B%E5%88%A4%E5%AE%9A%E8%A7%84%E5%88%99\"><span class=\"ez-toc-section\" id=\"Java%E4%B8%AD%E6%9D%A1%E4%BB%B6%E8%BF%90%E7%AE%97%E7%AC%A6%E7%9A%84%E7%BB%93%E6%9E%9C%E7%9A%84%E7%B1%BB%E5%9E%8B%E5%88%A4%E5%AE%9A%E8%A7%84%E5%88%99\"><\/span>Java\u4e2d\u6761\u4ef6\u8fd0\u7b97\u7b26\u7684\u7ed3\u679c\u7684\u7c7b\u578b\u5224\u5b9a\u89c4\u5219<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u8fd9\u771f\u662f\u94bb\u725b\u89d2\u5c16\u4e86\uff0c\u4e0d\u77e5\u9053\u4e3a\u4f55\u641e\u8fd9\u4e48\u590d\u6742\uff0c\u62ff\u53bb\u88c5\u903c\u8fd8\u4e0d\u9519\uff0c<a href=\"http:\/\/www.logicbig.com\/tutorials\/core-java-tutorial\/java-language\/ternary-numeric-rules\/\">\u4f20\u9001\u95e8<\/a>\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"%E5%8F%82%E8%80%83\"><span class=\"ez-toc-section\" id=\"%E5%8F%82%E8%80%83\"><\/span>\u53c2\u8003<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<ul class=\"wp-block-list\"><li><a href=\"http:\/\/www.logicbig.com\/tutorials\/core-java-tutorial\/java-language\/\">logicbig\u7684\u6559\u7a0b<\/a><\/li><li><a href=\"https:\/\/docs.oracle.com\/javase\/tutorial\/java\/generics\/index.html\">Oracle\u5173\u4e8e\u6cdb\u578b\u7684\u6559\u7a0b1<\/a><\/li><li><a href=\"https:\/\/docs.oracle.com\/javase\/tutorial\/extra\/generics\/index.html\">Oracle\u5173\u4e8e\u6cdb\u578b\u7684\u6559\u7a0b2<\/a><\/li><\/ul>\n","protected":false},"excerpt":{"rendered":"<p>\u603b\u662f\u60f3\u91cd\u65b0\u5b66\u4e60\u4e00\u904dJava\uff0c\u6216\u8005\u89c9\u5f97\u81ea\u5df1\u638c\u63e1\u4e0d\u591f\u624e\u5b9e\u60f3\u8865\u5168\u4e00\u4e0b\uff0c\u9664\u4e86Oracle\u7684\u5b98\u65b9\u6559\u7a0b\u5916\uff0c\u6700\u8fd1\u53d1\u73b0\u4e86logicbig.com\u8fd9\u4e2a\u7f51\u7ad9\uff0c\u4e0a\u9762\u7684\u57fa\u672c\u90fd\u5e26\u6709\u5b8c\u6574\u7684\u4ee3\u7801\u5b9e\u4f8b\uff0c\u8bb2\u89e3\u4e5f\u6e05\u695a\u7b80\u6d01\uff0c\u6392\u7248\u4e5f\u5f88\u597d\u770b\uff0c&#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10],"tags":[87],"class_list":["post-852","post","type-post","status-publish","format-standard","hentry","category-10","tag-java"],"_links":{"self":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts\/852","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=852"}],"version-history":[{"count":1,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts\/852\/revisions"}],"predecessor-version":[{"id":855,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts\/852\/revisions\/855"}],"wp:attachment":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=852"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=852"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=852"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}