{"id":5340,"date":"2022-05-01T18:05:59","date_gmt":"2022-05-01T10:05:59","guid":{"rendered":"https:\/\/www.xttblog.com\/?p=5340"},"modified":"2022-05-01T18:05:59","modified_gmt":"2022-05-01T10:05:59","slug":"%e6%94%b6%e8%97%8f%ef%bc%81%e7%ae%80%e5%8d%95%e4%b8%94%e4%bc%98%e9%9b%85%e7%9a%848%e7%a7%8d%e5%b9%b2%e6%8e%89if-else%e7%9a%84%e6%96%b9%e6%b3%95%e9%9d%9e%e8%ae%be%e8%ae%a1%e6%a8%a1%e5%bc%8f%e6%96%b9","status":"publish","type":"post","link":"https:\/\/www.xttblog.com\/?p=5340","title":{"rendered":"\u6536\u85cf\uff01\u7b80\u5355\u4e14\u4f18\u96c5\u76848\u79cd\u5e72\u6389if else\u7684\u65b9\u6cd5(\u975e\u8bbe\u8ba1\u6a21\u5f0f\u65b9\u6cd5)"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">2 \u5e74\u524d\uff0c\u6211\u5728 b \u7ad9\u4e0a\u5f55\u5236\u4e86\u4e00\u4e2a\u89c6\u9891\uff0c\u5982\u4f55\u4f18\u96c5\u7684\u5e72\u6389 if else\u3002\u6211\u5f53\u65f6\u63d0\u51fa\u4e86\u201c\u65ad\u8a00\u201d+\u201c\u77ed\u8def\u201d\u7684\u5f62\u5f0f\uff0c\u6700\u76f4\u63a5\u7684\u5e72\u6389 if else\u3002\u5f88\u591a\u4eba\u975e\u5e38\u53d7\u76ca\uff0c\u4eca\u5929\u6211\u518d\u6574\u7406\u6210\u6587\u5b57\u5206\u4eab\u7ed9\u5927\u5bb6\uff01<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">if else \u662f\u6211\u4eec\u5199\u4ee3\u7801\u65f6\uff0c\u4f7f\u7528\u9891\u7387\u6700\u9ad8\u7684\u5173\u952e\u8bcd\u4e4b\u4e00\uff0c\u7136\u800c\u6709\u65f6\u8fc7\u591a\u7684 if else \u4f1a\u8ba9\u6211\u4eec\u611f\u5230\u8111\u58f3\u75bc\uff0c\u4f8b\u5982\u4e0b\u9762\u8fd9\u4e2a\u4f2a\u4ee3\u7801\uff1a<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/cdn.jsdelivr.net\/gh\/xmt1139057136\/xttblog\/2022\/03\/if-else.png\" alt=\"if else \u591a\u5c42\u5d4c\u5957\" \/><figcaption>if else \u591a\u5c42\u5d4c\u5957<\/figcaption><\/figure>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/cdn.jsdelivr.net\/gh\/xmt1139057136\/xttblog\/2022\/03\/else-if.png\" alt=\"\u8d85\u590d\u6742\u7684if else\" \/><figcaption>\u8d85\u590d\u6742\u7684if else<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">\u662f\u4e0d\u662f\u5f88\u5954\u6e83\uff1f\u60f3\u8c61\u4f60\u73b0\u5728\u662f\u4e00\u4e2a\u65b0\u624b\u7a0b\u5e8f\u5458\uff0c\u6216\u8005\u662f\u4e00\u4e2a\u521a\u5165\u804c\u7684\u5c0f\u53f8\u673a\uff0c\u8fd9\u6837\u7684\u4ee3\u7801\uff0c\u4f60\u6562\u7ef4\u62a4\u5417\uff1f<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u57fa\u4e8e\u6b64\uff0c\u6211\u5728\u8fd9\u91cc\u63a8\u8350\u51e0\u79cd\u6d88\u9664 if else \u7684\u65b9\u6cd5\uff0c\u5e0c\u671b\u80fd\u591f\u5e2e\u52a9\u5230\u5927\u5bb6\uff01<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u591a\u4f7f\u7528\u201c\u65ad\u8def\u201dreturn<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>if(\"\u4e1a\u4f59\u8349\".equals(author)){\n  \/\/ ...\n  System.out.println(\"\u4f60\u597d\");\n}else if(\"\u5927\u4f6c\".equals(author)){\n  \/\/ ...\n  System.out.println(\"\u4f60\u597d\");\n} else {\n  throw new Exception(\"error\");\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0a\u9762\u8fd9\u4e48\u4ee3\u7801\uff0c\u6211\u4eec\u8fd9\u6837\u8fd9\u6837\u4fee\u6539\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if(\"\u4e1a\u4f59\u8349\".equals(author)){\n  \/\/ ...\n  System.out.println(\"\u4f60\u597d\");\n  return;\n}\n\nif(\"\u5927\u4f6c\".equals(author)){\n  \/\/ ...\n  System.out.println(\"\u4f60\u597d\");\n  return;\n} \n\nthrow new Exception(\"error\");<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5f53\u7136\uff0c\u6211\u8fd9\u4e2a\u6848\u4f8b\u5d4c\u5957\u7684\u5c42\u6b21\u592a\u5c11\uff0c\u90e8\u5206\u4eba\u611f\u89c9\u4e0d\u660e\u663e\u3002\u4e0b\u9762\u6211\u4eec\u4e00\u8d77\u770b\u4e00\u4e2a\u7a0d\u5fae\u590d\u6742\u4e00\u70b9\u7684\u6848\u4f8b\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>public String getTweetTitle(int type) {\n    String result;\n    if (type == 0) {\n        throw new IllegalArgumentException(\"\u53c2\u6570\u6709\u8bef\");\n    }\n\n    \/\/\u957f\u8d34--&gt;\u83b7\u5f97\u957f\u5e16\u6807\u9898\n    if (isPaperTweet(type)) {\n        result = getPaperTweetTitle();\n    } else {\n        \/\/ \u89c6\u9891\u8d34--&gt;\u83b7\u5f97\u89c6\u9891\u8d34\u6807\u9898\n        if (isVideoTweet(type)) {\n            result = getVideoTitle();\n        } else {\n            result = getDefaultTitle();\n        }\n    }\n    return result;\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u4eec\u4f7f\u7528\u201c\u65ad\u8def\u201d\u7684\u65b9\u6cd5\uff0c\u53ef\u4ee5\u6539\u6210\u5982\u4e0b\u65b9\u5f0f\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>public String getTweetTitle(int type) {\n    \/\/ \u6761\u4ef6\u68c0\u67e5\n    if (type == 0) {\n        throw new IllegalArgumentException(\"\u53c2\u6570\u6709\u8bef\");\n    }\n\n    \/\/ \u957f\u8d34--&gt;\u83b7\u5f97\u957f\u5e16\u6807\u9898\n    if (isPaperTweet(type)) {\n        return getPaperTweetTitle();\n    }\n\n    \/\/ \u89c6\u9891\u8d34--&gt;\u83b7\u5f97\u89c6\u9891\u8d34\u6807\u9898\n    if (isVideoTweet(type)) {\n        return getVideoTitle();\n    }\n\n    return getDefaultTitle();\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0a\u9762\u7684\u4ee3\u7801\u662f\u4e0d\u662f\u770b\u8d77\u6765\u66f4\u6e05\u723d\u4e00\u4e9b\uff01\u5b9e\u9645\u4e0a\uff0c\u963f\u91cc\u5df4\u5df4\u5f00\u53d1\u624b\u518c\u4e2d\u4e5f\u63a8\u8350\u6211\u8fd9\u79cd\u505a\u6cd5\u4e86\uff01<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img decoding=\"async\" src=\"https:\/\/cdn.jsdelivr.net\/gh\/xmt1139057136\/xttblog\/2022\/03\/if-else-if.png\" alt=\"\u300a\u963f\u91cc\u5df4\u5df4\u5f00\u53d1\u624b\u518c\u300b\u4e2d\uff0c\u5173\u4e8e\u591a if-else\u7684\u4f7f\u7528\u63a8\u8350\" \/><figcaption>\u300a\u963f\u91cc\u5df4\u5df4\u5f00\u53d1\u624b\u518c\u300b\u4e2d\uff0c\u5173\u4e8e\u591a if-else\u7684\u4f7f\u7528\u63a8\u8350<\/figcaption><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\">\u51cf\u5c11\u65e0\u7528\u7684 if else<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u4eec\u7ee7\u7eed\u63a5\u7740\u770b\u4e00\u4e2a\u4f8b\u5b50\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if(100 == age){\n  return true;\n} else {\n  return false;\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u8fd9\u662f\u6211\u5de5\u4f5c\u591a\u5e74\u6765\uff0c\u89c1\u5230\u4e0d\u5c11\u540c\u4e8b\u8fd9\u6837\u5199\u7684\uff08\u4e0d\u662f\u6545\u610f\u9ed1\u4ed6\u4eec\uff09\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u4eec\u53ef\u4ee5\u8fd9\u6837\u6539\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>return\u00a0100\u00a0==\u00a0age;<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u76f4\u63a5\u8fd4\u56de\u5224\u65ad\u7684\u7ed3\u679c\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u4f7f\u7528\u4e09\u5143\u8fd0\u7b97<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u5b9e\u9645\u4e0a\uff0c\u4ece\u6548\u7387\u4e0a\u6765\u8bb2\uff0c\u4e09\u5143\u8fd0\u7b97\u7684\u6548\u7387\u4e5f\u6bd4 if else \u9ad8\uff01<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if(age &gt; 18){\n  result = \"\u6210\u5e74\u4eba\u53ef\u4ee5\u6253\u6e38\u620f\u8d85\u8fc71\u4e2a\u5c0f\u65f6\";\n} else {\n  result = \"\u672a\u6210\u5e74\u4eba\u6253\u6e38\u620f\u4e0d\u80fd\u8d85\u8fc71\u4e2a\u5c0f\u65f6\";\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6539\u6210\u4e09\u5143\u8fd0\u7b97\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>result\u00a0=\u00a0age\u00a0&gt;\u00a018\u00a0?\u00a0\"\u6210\u5e74\u4eba\u53ef\u4ee5\u6253\u6e38\u620f\u8d85\u8fc71\u4e2a\u5c0f\u65f6\"\u00a0:\u00a0\"\u672a\u6210\u5e74\u4eba\u6253\u6e38\u620f\u4e0d\u80fd\u8d85\u8fc71\u4e2a\u5c0f\u65f6\";<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">\u591a\u4f7f\u7528\u65ad\u8a00<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u7ee7\u7eed\u770b\u4e0b\u9762\u8fd9\u4e2a\u4f8b\u5b50\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>if(null == name || \"\".equals(name)){\n  throw new Exception(\"\u59d3\u540d\u4e0d\u80fd\u4e3a\u7a7a\");\n}\n\nif(age &lt; 18){\n  throw new Exception(\"\u5e74\u9f84\u4e0d\u80fd\u5c0f\u4e8e18\");\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u4eec\u53ef\u4ee5\u6539\u6210\u4e0b\u9762\u7684\u5b9e\u73b0\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Assert.hasLength(name, \"\u59d3\u540d\u4e0d\u80fd\u4e3a\u7a7a\");\nAssert.isTrue(age &lt; 18, \"\u5e74\u9f84\u4e0d\u80fd\u5c0f\u4e8e18\");<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6216\u8005\u662f\u4f60\u81ea\u5df1\u5c01\u88c5\u4e00\u4e2a\u53c2\u6570\u6821\u9a8c\u65b9\u6cd5\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>public abstract class PreCheck {\n    public PreCheck() {\n    }\n\n    public static void preCheckNotNull(Object obj) {\n        if (obj == null) {\n            throw new ServerException(\"attr data cannot be empty\");\n        }\n    }\n\n    public static void preCheckNotNull(Object obj, String msg) {\n        if (obj == null) {\n            throw new ServerException(msg);\n        }\n    }\n\n    public static void preCheckNotNull(Object obj, ErrorMessage errorMessage) {\n        if (obj == null) {\n            throw new ServerException(errorMessage);\n        }\n    }\n\n    public static void preCheckArgument(boolean checked, String msg) {\n        if (checked) {\n            throw new ServerException(msg);\n        }\n    }\n\n    public static void preCheckArgument(boolean checked, ErrorMessage errorMessage) {\n        if (checked) {\n            throw new ServerException(errorMessage);\n        }\n    }\n\n    public static BigDecimal preCheckBigDecimal(String val, String msg) {\n        try {\n            return new BigDecimal(val);\n        } catch (Exception var3) {\n            throw new ServerException(msg);\n        }\n    }\n\n    public static BigDecimal preCheckBigDecimal(String val, ErrorMessage errorMessage) {\n        try {\n            return new BigDecimal(val);\n        } catch (Exception var3) {\n            throw new ServerException(errorMessage);\n        }\n    }\n    \n    \/\/ ...\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0a\u9762\u8fd9\u4e2a\u662f\u6211\u5e38\u7528\u7684\u4e00\u4e2a\u5de5\u5177\u7c7b\u3002<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">\u4f7f\u7528 map \u53d6\u4ee3 if else<\/h2>\n\n\n\n<pre class=\"wp-block-code\"><code>if (t == 1) {\n    type = \"\u767e\u5ea6\";\n} else if (t == 2) {\n    type = \"\u5b57\u8282\";\n} else if (t == 3) {\n    type = \"\u963f\u91cc\";\n} else if (t == 4) {\n    type = \"\u817e\u8baf\";\n}\n\/\/ ...<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u679c if \u592a\u591a\uff0c\u5c31\u663e\u5f97\u592a\u957f\u4e86\u3002\u6211\u89c1\u8fc7\u4e00\u4e2a if else if \u8d85\u8fc7 300 \u884c\u7684\u4ee3\u7801\u3002\u8fd9\u4e2a\u65f6\u5019\u4e09\u5143\u8fd0\u7b97\u7b26\u4e5f\u4e0d\u592a\u597d\u7528\u4e86\uff0c\u8fd9\u91cc\u6211\u63a8\u8350\u4f7f\u7528 map \u6765\u505a\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>Map&lt;Integer, String&gt; typeMap = new HashMap&lt;&gt;();\ntypeMap.put(1, \"\u767e\u5ea6\");\ntypeMap.put(2, \"\u5b57\u8282\");\ntypeMap.put(3, \"\u963f\u91cc\");\ntypeMap.put(4, \"\u817e\u8baf\");\n\/\/ ...\n\nreturn typeMap.get(type);<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">\u51cf\u5c11\u6ca1\u5fc5\u8981\u7684 if<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e00\u4e9b\u4ee3\u7801\u6211\u4eec\u8981\u5408\u7406\u7684\u62bd\u53d6\uff0c\u63d0\u51fa\u516c\u5171\u7684\u90e8\u5206\u3002\u4e0b\u9762\u6211\u4eec\u518d\u770b\u4e00\u4e2a\u4f8b\u5b50\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String result = \"\";\nif(age == 1){\n  \/\/ todo \n  result = \"\u5e74\u9f84\u592a\u5c0f\u4e86\";\n}\n\nif(age == 2){\n  \/\/ todo \n  result = \"\u5e74\u9f84\u592a\u5c0f\u4e86\";\n}\n\n\/\/ ...<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e0a\u9762\u7684\u4ee3\u7801\u6211\u4eec\u53ef\u4ee5\u5c06\u4e24\u4e2a if \u8fdb\u884c\u5408\u5e76\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String result = \"\";\nif(age == 1 || age == 2){\n  \/\/ todo \n  result = \"\u5e74\u9f84\u592a\u5c0f\u4e86\";\n}\n\/\/ ...<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5f53\u7136\uff0c\u5982\u679c\u662f\u4e00\u4e2a\u8303\u56f4\uff0c\u4e5f\u53ef\u4ee5\u8fdb\u884c\u8303\u56f4\u5224\u65ad\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String result = \"\";\nif(age &gt; 0 || age &lt; 12){\n  \/\/ todo \n  result = \"\u5e74\u9f84\u592a\u5c0f\u4e86\";\n}\n\/\/ ...<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">\u53cd\u5411\u903b\u8f91\u51cf\u5c11 if else<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">\u591a\u6570\u60c5\u51b5\u4e0b\uff0c\u6211\u4eec\u5199\u4ee3\u7801\u90fd\u662f\u6b63\u5411\u903b\u8f91\u3002\u4e0b\u9762\u6211\u901a\u8fc7\u4e00\u4e9b\u53cd\u5411\u903b\u8f91\u51cf\u5c11\u4e00\u4e9b if else\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ \u65b9\u6cd5 A\nList&lt;DocFieldDto&gt; list = dto.getDocFieldDtoList();\nif (!CollectionUtils.isEmpty(list)) {\n    \/\/ todo ...\n}\n\n\/\/ \u65b9\u6cd5 B\nif(a != null){\n  \/\/ todo\n  if(b != null){\n    \/\/ todo\n  }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u4eec\u53ef\u4ee5\u5229\u7528\u53cd\u5411\u903b\u8f91\u8fdb\u884c\u4ee3\u7801\u7cbe\u7b80\u6539\u9020\uff01<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>\/\/ \u65b9\u6cd5 A\nList&lt;DocFieldDto&gt; list = dto.getDocFieldDtoList();\nif(CollectionUtils.isEmpty(list)){\n  return;\n}\n\n\/\/ \u65b9\u6cd5 B\nif(null == a){\n  return;\n}\n\n\/\/ todo\nif(b == null){\n  return;\n}\n\/\/ todo<\/code><\/pre>\n\n\n\n<h2 class=\"wp-block-heading\">\u591a\u4f7f\u7528 Optional<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Optional \u8fd8\u662f\u5f88\u597d\u7528\u7684\uff0c\u6211\u4e2a\u4eba\u975e\u5e38\u559c\u6b22\u7528\u3002\u7ee7\u7eed\u770b\u4e0b\u9762\u8fd9\u4e2a\u4f8b\u5b50\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String str = \"java\u548c\u524d\u7aef\u90fd\u96be\";\nif (str == null) {\n    System.out.println(\"null\");\n} else {\n    System.out.println(str);\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u6211\u4eec\u53ef\u4ee5\u8fd9\u6837\u6539\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String str2 = \"java\u548c\u524d\u7aef\u90fd\u96be\";\nString result = Optional.ofNullable(str2).orElse(\"null\");\nSystem.out.println(result);\n\n\/\/\u8f93\u51fa\uff1ajava\u548c\u524d\u7aef\u90fd\u96be\n\n\/\/\u7b49\u540c\u4e8e:\nif (str2 != null) {\n    System.out.println(str2);\n} else {\n    System.out.println(\"null\");\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u518d\u6bd4\u5982\uff0c\u6211\u4eec\u901a\u5e38\u6709\u4e00\u4e2a\u5bf9\u8c61\uff0c\u9700\u8981\u4e00\u5c42\u4e00\u5c42\u7684\u53bb\u5224\u65ad\u53d6\u503c\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String isocode = user.getAddress().getCountry().getIsocode().toUpperCase();\n\n\/\/ \u6216\u8005\u6709\u4e9b\u7a0b\u5e8f\u5458\u52a0\u4e0a\u4e86\u5224\u65ad\nif (user != null) {\n    Address address = user.getAddress();\n    if (address != null) {\n        Country country = address.getCountry();\n        if (country != null) {\n            String isocode = country.getIsocode();\n            if (isocode != null) {\n                isocode = isocode.toUpperCase();\n            }\n        }\n    }\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5982\u679c\u7528 Optional\uff0c\u770b\u8d77\u6765\u5c31\u66f4\u8212\u670d\u4e86\u3002<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>@Test\npublic void whenChaining_thenOk() {\n    User user = new User(\"anna@gmail.com\", \"1234\");\n\n    String result = Optional.ofNullable(user)\n      .flatMap(u -&gt; u.getAddress())\n      .flatMap(a -&gt; a.getCountry())\n      .map(c -&gt; c.getIsocode())\n      .orElse(\"default\");\n\n    assertEquals(result, \"default\");\n}<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4e5f\u53ef\u4ee5\u901a\u8fc7\u65b9\u6cd5\u5f15\u7528\u8fdb\u4e00\u6b65\u7f29\u51cf\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>String result = Optional.ofNullable(user)\n  .flatMap(User::getAddress)\n  .flatMap(Address::getCountry)\n  .map(Country::getIsocode)\n  .orElse(\"default\");<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5f53\u7136\uff0cOptional \u5728\u67d0\u4e9b\u573a\u666f\u4e0b\u662f\u4e0d\u80fd\u591f\u5b8c\u5168\u4ee3\u66ff if else \u7684\uff0c\u8fd9\u70b9\u89c6\u60c5\u51b5\u81ea\u884c\u5224\u65ad\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u4ee5\u4e0a\u5c31\u662f\u6211\u4eec\u7ecf\u5e38\u4f7f\u7528\u7684\u7f29\u51cf if else \u7684\u5c0f\u5999\u62db\u3002\u4e0d\u559c\u8f7b\u55b7\uff01<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u9664\u6b64\u4e4b\u5916\uff0c\u5f88\u591a\u4eba\u53ef\u80fd\u8fd8\u770b\u5230\u8fc7\u5404\u79cd\u8bbe\u8ba1\u6a21\u5f0f\u5e72\u6389 if else \u7684\uff0c\u6211\u5c31\u4e0d\u591a\u8bf4\u4e86\u3002\u5305\u62ec\uff1a\u591a\u6001\u3001\u53cd\u5c04\u3001\u679a\u4e3e\u3001\u7b56\u7565\u6a21\u5f0f\u7b49\u4e0d\u5728\u672c\u6587\u7684\u8ba8\u8bba\u8303\u56f4\u5185\u3002<\/p>\n<!-- <audio autoplay=\"autoplay\" height=\"100\" width=\"100\" hidden=\"true\"><source src=\"https:\/\/c.coka.la\/orAvPR.mp3\" type=\"audio\/mp3\"\/><\/audio><img decoding=\"async\" src=\"https:\/\/images.weserv.nl\/?url=https:\/\/ws3.sinaimg.cn\/large\/8fa5dcfcgy1g4em3rzar5j20ib089ae0.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/> --><p><!-- <img decoding=\"async\" src=\"https:\/\/raw.githubusercontent.com\/xmt1139057136\/xttblog\/master\/8fa5dcfcgy1g4em3rzar5j20ib089ae0.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/>--><img decoding=\"async\" src=\"https:\/\/saas.51autoparts.cn\/api\/admin\/sys-file\/oss\/file?fileName=84db51f8561e448f9a4fda2eff0811f9.jpg\" alt=\"\u4e1a\u4f59\u8349\u516c\u4f17\u53f7\"\/><\/p><p>\u6700\u540e\uff0c\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u4e2a\u4eba\u5fae\u4fe1\u516c\u4f17\u53f7\uff1a\u4e1a\u4f59\u8349\uff08yyucao\uff09\uff01<b>\u53ef\u52a0\u4f5c\u8005\u5fae\u4fe1\u53f7\uff1a<font color=\"red\">xttblog2<\/font>\u3002\u5907\u6ce8\uff1a\u201c1\u201d\uff0c\u6dfb\u52a0\u535a\u4e3b\u5fae\u4fe1\u62c9\u4f60\u8fdb\u5fae\u4fe1\u7fa4\u3002\u5907\u6ce8\u9519\u8bef\u4e0d\u4f1a\u540c\u610f\u597d\u53cb\u7533\u8bf7\u3002<\/b>\u518d\u6b21\u611f\u8c22\u60a8\u7684\u5173\u6ce8\uff01\u540e\u7eed\u6709\u7cbe\u5f69\u5185\u5bb9\u4f1a\u7b2c\u4e00\u65f6\u95f4\u53d1\u7ed9\u60a8\uff01\u539f\u521b\u6587\u7ae0\u6295\u7a3f\u8bf7\u53d1\u9001\u81f3532009913@qq.com\u90ae\u7bb1\u3002\u5546\u52a1\u5408\u4f5c\u4e5f\u53ef\u6dfb\u52a0\u4f5c\u8005\u5fae\u4fe1\u8fdb\u884c\u8054\u7cfb\uff01<\/p><p>\u672c\u6587\u539f\u6587\u51fa\u5904\uff1a<a href=\"https:\/\/www.xttblog.com\">\u4e1a\u4f59\u8349<\/a>\uff1a &raquo; <a href=\"https:\/\/www.xttblog.com\/?p=5340\">\u6536\u85cf\uff01\u7b80\u5355\u4e14\u4f18\u96c5\u76848\u79cd\u5e72\u6389if else\u7684\u65b9\u6cd5(\u975e\u8bbe\u8ba1\u6a21\u5f0f\u65b9\u6cd5)<\/a><\/p><!-- <div class=\"bd-reward-stl\"><button id=\"bdRewardBtn\"><span><\/span><\/button><\/div> -->","protected":false},"excerpt":{"rendered":"<p>2 \u5e74\u524d\uff0c\u6211\u5728 b \u7ad9\u4e0a\u5f55\u5236\u4e86\u4e00\u4e2a\u89c6\u9891\uff0c\u5982\u4f55\u4f18\u96c5\u7684\u5e72\u6389 if else\u3002\u6211\u5f53\u65f6\u63d0\u51fa\u4e86\u201c\u65ad\u8a00\u201d+\u201c\u77ed\u8def\u201d\u7684\u5f62\u5f0f\uff0c [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":336,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[391,79,2076,76,104,1143],"class_list":["post-5340","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-java","tag-mysql","tag-79","tag-2076","tag-76","tag-104","tag-1143"],"_links":{"self":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/5340","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5340"}],"version-history":[{"count":1,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/5340\/revisions"}],"predecessor-version":[{"id":5341,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/posts\/5340\/revisions\/5341"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=\/wp\/v2\/media\/336"}],"wp:attachment":[{"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5340"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5340"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.xttblog.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5340"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}