{"id":31230,"date":"2024-02-02T06:22:49","date_gmt":"2023-03-23T14:36:03","guid":{"rendered":"https:\/\/www.silicloud.com\/zh\/blog\/%e5%9c%a8java8%e4%b8%ad%ef%bc%8c%e7%bc%96%e5%86%99%e7%b1%bb%e4%bc%bcjava8%e9%a3%8e%e6%a0%bc%e7%9a%84%e4%bb%a3%e7%a0%81%e3%80%82\/"},"modified":"2025-08-12T22:57:59","modified_gmt":"2025-08-12T14:57:59","slug":"%e5%9c%a8java8%e4%b8%ad%ef%bc%8c%e7%bc%96%e5%86%99%e7%b1%bb%e4%bc%bcjava8%e9%a3%8e%e6%a0%bc%e7%9a%84%e4%bb%a3%e7%a0%81%e3%80%82","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/zh\/blog\/%e5%9c%a8java8%e4%b8%ad%ef%bc%8c%e7%bc%96%e5%86%99%e7%b1%bb%e4%bc%bcjava8%e9%a3%8e%e6%a0%bc%e7%9a%84%e4%bb%a3%e7%a0%81%e3%80%82\/","title":{"rendered":"\u5728Java8\u4e2d\uff0c\u7f16\u5199\u7c7b\u4f3cJava8\u98ce\u683c\u7684\u4ee3\u7801"},"content":{"rendered":"<h1>\u603b\u7ed3\u4e00\u4e0b(\u4f60\u5728\u8bf4\u4ec0\u4e48\u5462)<\/p>\n<ul class=\"post-ul\">\n\u30b3\u30fc\u30c9\u30ec\u30d3\u30e5\u30fc\u3057\u3066\u3044\u308b\u3068\u3001Java8\u306efeature(Stream API\u3068\u304bOptional\u3068\u304b)\u3092\u4f7f\u3063\u3066\u308b\u3093\u3060\u3051\u3069\u3001Java7\u4ee5\u524d\u3068\u5927\u5dee\u306a\u3044\u66f8\u304d\u65b9\u3092\u3055\u308c\u3066\u3044\u308b\u30b3\u30fc\u30c9\u3092\u3088\u304f\u898b\u304b\u3051\u308b\u3002<br \/>\n\u3082\u3063\u3068\u7686\u306bJava8\u3063\u307d\u3044\u30b3\u30fc\u30c9\u3092\u66f8\u3044\u3066\u6b32\u3057\u3044\u3002\u305d\u3046\u3058\u3083\u306a\u3044\u3068\u3082\u3063\u305f\u3044\u306a\u3044\u3002<br \/>\n(*&#8221;Java8\u3063\u307d\u3044&#8221;\u306e\u57fa\u6e96\u306f\u5272\u308a\u3068(\u304b\u306a\u308a?)\u79c1\u898b\u304c\u5165\u3063\u3066\u3044\u308b)<br \/>\n\u8a00\u8449\u3092\u5c3d\u304f\u3057\u3066\u3082\u4f1d\u308f\u308a\u3065\u3089\u3044\u306e\u3067\u3001\u4f8b\u3092\u4f5c\u308d\u3046\u3002 \u2190 \u3053\u308c<\/p>\n<p>\u3064\u3044\u3067\u306b\u3001\u300c\u7121\u7406\u3057\u3066Java8\u306efeature\u4f7f\u3046\u3053\u3068\u3067\u3001\u9006\u306b\u60aa\u304f\u306a\u3063\u3066\u3057\u307e\u3063\u3066\u3044\u308b\u4f8b\u300d\u3082\u4f5c\u308d\u3046\u3002<\/p>\n<\/ul>\n<h2>\u76ee\u6807\u8bfb\u8005<\/p>\n<ul class=\"post-ul\">\nJava8\u3067\u30b3\u30fc\u30c9\u66f8\u3044\u3066\u308b\u3051\u3069\u3001Java7\u4ee5\u524d\u306e\u66f8\u304d\u65b9\u304c\u67d3\u307f\u4ed8\u3044\u3061\u3083\u3063\u3066\u3044\u3066\u306a\u304b\u306a\u304b\u629c\u3051\u51fa\u305b\u306a\u3044\u4eba<br \/>\n\u300cfor\u3084null\u30c1\u30a7\u30c3\u30af\u306f\u7d76\u5bfe\u4f7f\u3046\u3079\u304d\u3067\u306a\u3044\u300d\u3068\u3044\u3046\u601d\u3044\u304c\u5f37\u3059\u304e\u3066\u3001\u4f55\u3067\u3082\u304b\u3093\u3067\u3082Stream API\u3084Optional\u4f7f\u3063\u3066\u308b\u4eba\n<\/ul>\n<h2>\u901a\u77e5<\/p>\n<p>\u8fd9\u7bc7\u6587\u7ae0\u4e2d\u6240\u5199\u7684\u5185\u5bb9\u5e76\u6ca1\u6709\u4ec0\u4e48\u7279\u522b\u65b0\u5947\u7684\uff0c\u800c\u4e14\u9664\u4e86Java\u4e4b\u5916\u7684\u8bed\u8a00\u4e5f\u53ef\u4ee5\u6709\u66f4\u52a0\u7cbe\u7ec3\u7684\u8868\u8fbe\u65b9\u5f0f\u3002\u8fd9\u7bc7\u6587\u7ae0\u53ea\u662f\u9488\u5bf9\u90a3\u4e9b\u4eceJava7\u8fc1\u79fb\u5230Java8\u4f46\u5bf9Stream\u548cOptional\u7684\u4f7f\u7528\u65b9\u5f0f\u4e0d\u719f\u6089\u7684\u4eba\u6240\u5199\u7684\u3002<\/p>\n<h1>\u80fd\u591f\u66f4\u52a0\u7b26\u5408Java8\u98ce\u683c\u7684\u6a21\u5f0f<\/p>\n<p>\u6709\u4e00\u4e2a\u7c7b\u4f3c\u7684\u4ea7\u54c1\u5bf9\u8c61\uff0c\u5e76\u5047\u8bbe\u6211\u4eec\u8981\u5bf9\u5176\u8fdb\u884c\u67d0\u79cd\u5904\u7406\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"c1\">\/\/ \u5546\u54c1\u30af\u30e9\u30b9<\/span>\r\n<span class=\"kd\">public<\/span> <span class=\"kd\">class<\/span> <span class=\"nc\">Item<\/span> <span class=\"o\">{<\/span>\r\n  <span class=\"nc\">String<\/span> <span class=\"n\">name<\/span><span class=\"o\">;<\/span> <span class=\"c1\">\/\/ \u5546\u54c1\u540d<\/span>\r\n  <span class=\"nc\">BigDecimal<\/span> <span class=\"n\">price<\/span><span class=\"o\">;<\/span> <span class=\"c1\">\/\/ \u5546\u54c1\u306e\u4fa1\u683c<\/span>\r\n  <span class=\"nc\">String<\/span> <span class=\"n\">currency<\/span><span class=\"o\">;<\/span> <span class=\"c1\">\/\/ price\u30d5\u30a3\u30fc\u30eb\u30c9\u306e\u901a\u8ca8(\"JPY\"\u3068\u304b\"USD\")<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<h2>\u53ea\u662f\u5c06\u589e\u5f3afor\u5faa\u73af\u7528forEach\u66ff\u6362\u4e86\u3002<\/p>\n<p>\u60f3\u8981\u8fdb\u884c\u5c06\u67d0\u4e9b\u6570\u636e\u8f6c\u6362\u5e76\u5b58\u50a8\u5230\u53e6\u4e00\u4e2a\u5217\u8868\u7684\u5904\u7406\u3002<br \/>\n\u5728Java7\u4e4b\u524d\uff0c\u53ef\u4ee5\u8fd9\u6837\u5199\uff1a<\/p>\n<pre class=\"post-pre\"><code><span class=\"c1\">\/\/ \u65e5\u672c\u5186\u306e\u5546\u54c1\u3092USD\u306b\u5909\u63db<\/span>\r\n<span class=\"nc\">BigDecimal<\/span> <span class=\"n\">jpyToUsd<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">BigDecimal<\/span><span class=\"o\">.<\/span><span class=\"na\">valueOf<\/span><span class=\"o\">(<\/span><span class=\"mi\">100<\/span><span class=\"o\">);<\/span>\r\n\r\n<span class=\"nc\">List<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Item<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">usdItems<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">ArrayList<\/span><span class=\"o\">&lt;&gt;();<\/span>\r\n\r\n<span class=\"k\">for<\/span><span class=\"o\">(<\/span><span class=\"nc\">Item<\/span> <span class=\"n\">jpyItem<\/span> <span class=\"o\">:<\/span> <span class=\"n\">jpyItems<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"nc\">Item<\/span> <span class=\"n\">usdItem<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">Item<\/span><span class=\"o\">();<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setName<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setPrice<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getPrice<\/span><span class=\"o\">().<\/span><span class=\"na\">multiply<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyToUsd<\/span><span class=\"o\">));<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setCurrency<\/span><span class=\"o\">(<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n    <span class=\"n\">usdItems<\/span><span class=\"o\">.<\/span><span class=\"na\">add<\/span><span class=\"o\">(<\/span><span class=\"n\">usdItem<\/span><span class=\"o\">);<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u6240\u4ee5\uff0c\u88ab\u544a\u77e5\u201c\u65e2\u7136\u662fJava8\uff0c\u5c31\u7528Stream\u800c\u4e0d\u662f\u4f7f\u7528for\u5faa\u73af\u201d\u4e4b\u540e\uff0c\u7ed3\u679c\u5c31\u662f\u8fd9\u6837\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">BigDecimal<\/span> <span class=\"n\">jpyToUsd<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">BigDecimal<\/span><span class=\"o\">.<\/span><span class=\"na\">valueOf<\/span><span class=\"o\">(<\/span><span class=\"mi\">100<\/span><span class=\"o\">);<\/span>\r\n\r\n<span class=\"nc\">List<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Item<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">usdItems<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">ArrayList<\/span><span class=\"o\">&lt;&gt;();<\/span>\r\n\r\n<span class=\"n\">jpyItems<\/span><span class=\"o\">.<\/span><span class=\"na\">forEach<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"nc\">Item<\/span> <span class=\"n\">usdItem<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">Item<\/span><span class=\"o\">();<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setName<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setPrice<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getPrice<\/span><span class=\"o\">().<\/span><span class=\"na\">multiply<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyToUsd<\/span><span class=\"o\">));<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setCurrency<\/span><span class=\"o\">(<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n    <span class=\"n\">usdItems<\/span><span class=\"o\">.<\/span><span class=\"na\">add<\/span><span class=\"o\">(<\/span><span class=\"n\">usdItem<\/span><span class=\"o\">);<\/span>\r\n<span class=\"o\">});<\/span>\r\n<\/code><\/pre>\n<p>\u505a\u7684\u4e8b\u60c5\u5e76\u6ca1\u6709\u5b8c\u5168\u6539\u53d8\uff0c\u53ea\u662f\u5c06\u5176\u91cd\u5199\u4e3a\u6d41\u7684\u201c\u4e2d\u95f4\u64cd\u4f5c\u201d\u548c\u201c\u7ec8\u7aef\u64cd\u4f5c\u201d\u8fd9\u6837\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">BigDecimal<\/span> <span class=\"n\">jpyToUsd<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">BigDecimal<\/span><span class=\"o\">.<\/span><span class=\"na\">valueOf<\/span><span class=\"o\">(<\/span><span class=\"mi\">100<\/span><span class=\"o\">);<\/span>\r\n\r\n<span class=\"c1\">\/\/ forEach\u3092\u4f7f\u308f\u305a\u3001map\u3068collect\u306e\u7d44\u307f\u5408\u308f\u305b\u3067\u5b9f\u73fe<\/span>\r\n<span class=\"nc\">List<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Item<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">usdItems<\/span> <span class=\"o\">=<\/span> <span class=\"n\">jpyItems<\/span><span class=\"o\">.<\/span><span class=\"na\">stream<\/span><span class=\"o\">()<\/span>\r\n        <span class=\"o\">.<\/span><span class=\"na\">map<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"o\">{<\/span>\r\n            <span class=\"nc\">Item<\/span> <span class=\"n\">usdItem<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">Item<\/span><span class=\"o\">();<\/span>\r\n            <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setName<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n            <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setPrice<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getPrice<\/span><span class=\"o\">().<\/span><span class=\"na\">multiply<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyToUsd<\/span><span class=\"o\">));<\/span>\r\n            <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setCurrency<\/span><span class=\"o\">(<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n\r\n            <span class=\"k\">return<\/span> <span class=\"n\">usdItem<\/span><span class=\"o\">;<\/span>\r\n        <span class=\"o\">})<\/span>\r\n        <span class=\"o\">.<\/span><span class=\"na\">collect<\/span><span class=\"o\">(<\/span><span class=\"nc\">Collectors<\/span><span class=\"o\">.<\/span><span class=\"na\">toList<\/span><span class=\"o\">());<\/span>\r\n<\/code><\/pre>\n<p>\u5173\u4e8emap\u4e2d\u7684\u5185\u5bb9\u53d8\u5f97\u81c3\u80bf\u7684\u89e3\u51b3\u65b9\u6848\u5c06\u5728\u540e\u9762\u8ba8\u8bba\u3002<\/p>\n<p>\u901a\u8fc7\u8fd9\u6837\u505a\uff0c<\/p>\n<ul class=\"post-ul\">\n\u3042\u308b\u30c7\u30fc\u30bf\u3092\u5909\u63db\u3057\u3066\u5225\u306e\u30c7\u30fc\u30bf\u3092\u751f\u6210\u3057\u3066\u3044\u308b(map(&#8230;))<br \/>\n\u5909\u63db\u3055\u308c\u305f\u30c7\u30fc\u30bf\u3092\u307e\u3068\u3081\u3066Collection\u306b\u3057\u3066\u3044\u308b(collect(&#8230;))\n<\/ul>\n<p>\u7531\u4e8e\u8fd9\u6837\u505a\u66f4\u52a0\u660e\u786e\uff0c\u53ef\u63d0\u9ad8\u53ef\u8bfb\u6027\u3002<br \/>\n\u867d\u7136forEach\u5f88\u65b9\u4fbf\u4e14\u80fd\u505a\u4efb\u4f55\u4e8b\u60c5\uff0c\u4f46\u4e5f\u5e94\u601d\u8003\u662f\u5426\u6709\u5176\u4ed6\u9002\u5408\u7684\u65b9\u6cd5\u3002<\/p>\n<h2>lambda\u5f88\u5927\u7684<\/p>\n<p>\u5728\u5148\u524d\u7684\u4f8b\u5b50\u4e2d\uff0cmap\u51fd\u6570\u4e2d\u7684lambda\u51fd\u6570\u5f88\u5e9e\u5927\uff0c\u800cStream\u7684\u65b9\u6cd5\u94fe\u53d8\u5f97\u5f88\u957f\uff0c\u5bfc\u81f4\u6574\u4f53\u4e0d\u591f\u6e05\u6670\uff0c\u53ef\u8bfb\u6027\u8f83\u4f4e\u3002<\/p>\n<p>\u5982\u679c\u6211\u4eec\u5c06lambda\u4f5c\u4e3a\u4e00\u4e2a\u53d8\u91cf\u63d0\u53d6\u51fa\u6765\uff0c\u90a3\u4e48\u5c31\u4f1a\u53d8\u6210\u8fd9\u6837\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"nc\">Function<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Item<\/span><span class=\"o\">,<\/span><span class=\"nc\">Item<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">convertToUsdItem<\/span> <span class=\"o\">=<\/span> <span class=\"n\">jpyItem<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"nc\">Item<\/span> <span class=\"n\">usdItem<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">Item<\/span><span class=\"o\">();<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setName<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setPrice<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getPrice<\/span><span class=\"o\">().<\/span><span class=\"na\">multiply<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyToUsd<\/span><span class=\"o\">));<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setCurrency<\/span><span class=\"o\">(<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n\r\n    <span class=\"k\">return<\/span> <span class=\"n\">usdItem<\/span><span class=\"o\">;<\/span>\r\n<span class=\"o\">};<\/span>\r\n\r\n<span class=\"nc\">List<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Item<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">usdItems<\/span> <span class=\"o\">=<\/span> <span class=\"n\">jpyItems<\/span><span class=\"o\">.<\/span><span class=\"na\">stream<\/span><span class=\"o\">()<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">map<\/span><span class=\"o\">(<\/span><span class=\"n\">convertToUsdItem<\/span><span class=\"o\">)<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">collect<\/span><span class=\"o\">(<\/span><span class=\"nc\">Collectors<\/span><span class=\"o\">.<\/span><span class=\"na\">toList<\/span><span class=\"o\">());<\/span>\r\n<\/code><\/pre>\n<p>\u5c3d\u7ba1\u8fd9\u6837\u4e5f\u80fd\u8ba9\u6d41\u7a0b\u66f4\u6e05\u6670\uff0c\u4f46\u662f\u5982\u679c\u4ee5\u540e\u60f3\u8981\u6d4b\u8bd5convertToUsdItem\u7684\u5904\u7406\u8fc7\u7a0b\u65f6\uff0c\u53ef\u6d4b\u8bd5\u6027\u4f1a\u5f88\u4f4e\u3002\u6240\u4ee5\u5c06\u5176\u8bbe\u4e3a\u901a\u5e38\u7684\u65b9\u6cd5\u4f1a\u66f4\u65b9\u4fbf\uff0c\u800c\u4e14\u4e2a\u4eba\u89c9\u5f97\u66f4\u6613\u8bfb\u3002 (\u81f3\u4e8e\u53ef\u8bfb\u6027\u53ef\u80fd\u662f\u4e2a\u4eba\u559c\u597d\u7684\u95ee\u9898)<\/p>\n<pre class=\"post-pre\"><code><span class=\"kd\">public<\/span> <span class=\"nc\">Item<\/span> <span class=\"nf\">convertToUsdItem<\/span><span class=\"o\">(<\/span><span class=\"nc\">Item<\/span> <span class=\"n\">jpyItem<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"nc\">Item<\/span> <span class=\"n\">usdItem<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">Item<\/span><span class=\"o\">();<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setName<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setPrice<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyItem<\/span><span class=\"o\">.<\/span><span class=\"na\">getPrice<\/span><span class=\"o\">().<\/span><span class=\"na\">multiply<\/span><span class=\"o\">(<\/span><span class=\"n\">jpyToUsd<\/span><span class=\"o\">));<\/span>\r\n    <span class=\"n\">usdItem<\/span><span class=\"o\">.<\/span><span class=\"na\">setCurrency<\/span><span class=\"o\">(<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n\r\n    <span class=\"k\">return<\/span> <span class=\"n\">usdItem<\/span><span class=\"o\">;<\/span>\r\n<span class=\"o\">}<\/span>\r\n\r\n<span class=\"nc\">List<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">Item<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">usdItems<\/span> <span class=\"o\">=<\/span> <span class=\"n\">jpyItems<\/span><span class=\"o\">.<\/span><span class=\"na\">stream<\/span><span class=\"o\">()<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">map<\/span><span class=\"o\">(<\/span><span class=\"k\">this<\/span><span class=\"o\">::<\/span><span class=\"n\">convertToUsdItem<\/span><span class=\"o\">)<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">collect<\/span><span class=\"o\">(<\/span><span class=\"nc\">Collectors<\/span><span class=\"o\">.<\/span><span class=\"na\">toList<\/span><span class=\"o\">());<\/span>\r\n<\/code><\/pre>\n<p>\u5982\u679c\u4f7f\u7528\u65b9\u6cd5\u5f15\u7528\uff0c\u53ef\u4ee5\u50cf\u4f7f\u7528lambda\u4e00\u6837\u7b80\u6d01\u5730\u7f16\u5199Stream\u3002<\/p>\n<h2>\u53ea\u4f7f\u7528\u4e86\u5bf9\u8c61\u7684\u90e8\u5206\u5b57\u6bb5\uff0c\u4f46\u6ca1\u6709\u8fdb\u884c\u6620\u5c04\u3002<\/p>\n<p>\u5f53\u8003\u8651\u50cf&#8221;\u4ee5&#8221;A&#8221;\u5f00\u5934\u7684\u5546\u54c1\u540d\u79f0\u4e3a\u4f8b\uff0c\u5c06\u5546\u54c1\u540d\u79f0\u8f93\u51fa\u5230\u6807\u51c6\u8f93\u51fa&#8221;\u8fd9\u6837\u7684\u5904\u7406\u65f6\uff0c\u5076\u5c14\u4f1a\u770b\u5230\u7c7b\u4f3c\u8fd9\u6837\u7684\u4ee3\u7801\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">steam<\/span><span class=\"o\">()<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">filter<\/span><span class=\"o\">(<\/span><span class=\"n\">item<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"n\">item<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">().<\/span><span class=\"na\">startsWith<\/span><span class=\"o\">(<\/span><span class=\"s\">\"A\"<\/span><span class=\"o\">))<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">forEach<\/span><span class=\"o\">(<\/span><span class=\"n\">item<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"nc\">System<\/span><span class=\"o\">.<\/span><span class=\"na\">out<\/span><span class=\"o\">.<\/span><span class=\"na\">println<\/span><span class=\"o\">(<\/span><span class=\"n\">item<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">()));<\/span>\r\n<\/code><\/pre>\n<p>\u53ea\u9700\u4f7f\u7528\u5546\u54c1\u540d\u79f0\uff0c\u4e0d\u9700\u8981\u4e00\u76f4\u4f20\u9012item\u5bf9\u8c61\uff0c\u6240\u4ee5\u6700\u597d\u5728\u5f00\u59cb\u65f6\u4f7f\u7528map\u63d0\u53d6\u51faname\u5b57\u6bb5\uff0c\u8fd9\u6837\u540e\u7eed\u5904\u7406\u4f1a\u66f4\u7b80\u5355\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">stream<\/span><span class=\"o\">()<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">map<\/span><span class=\"o\">(<\/span><span class=\"nl\">Item:<\/span><span class=\"o\">:<\/span><span class=\"n\">getName<\/span><span class=\"o\">)<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">filter<\/span><span class=\"o\">(<\/span><span class=\"n\">name<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"n\">name<\/span><span class=\"o\">.<\/span><span class=\"na\">startsWith<\/span><span class=\"o\">(<\/span><span class=\"s\">\"A\"<\/span><span class=\"o\">))<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">forEach<\/span><span class=\"o\">(<\/span><span class=\"nc\">System<\/span><span class=\"o\">.<\/span><span class=\"na\">out<\/span><span class=\"o\">::<\/span><span class=\"n\">println<\/span><span class=\"o\">);<\/span>\r\n<\/code><\/pre>\n<p>\u901a\u8fc7\u8fd9\u6837\u505a\uff0c<\/p>\n<ul class=\"post-ul\">\n\u201d\u5546\u54c1\u540d\u306e\u307f\u3092\u6271\u3046\u201d\u3068\u3044\u3046\u3053\u3068\u304c\u65e9\u3044\u6bb5\u968e\u3067\u7406\u89e3\u3067\u304d\u308b<br \/>\n\u30e1\u30bd\u30c3\u30c9\u53c2\u7167\u306b\u3088\u308a\u30b3\u30fc\u30c9\u3092\u3088\u308a\u30b7\u30f3\u30d7\u30eb\u306b\u3067\u304d\u308b\n<\/ul>\n<p>\u62e5\u6709\u4ee5\u4e0b\u7684\u597d\u5904\u3002<\/p>\n<h2>\u5728\u521b\u5efa\u4e00\u4e2a\u8fd4\u56denull\u7684\u65b9\u6cd5\uff0c\u5e76\u5728\u8c03\u7528\u8be5\u65b9\u6cd5\u7684\u5730\u65b9\u8fdb\u884cnull\u68c0\u67e5\u3002<\/p>\n<p>\u5728\u5904\u7406Stream API\u7684findFirst\u65b9\u6cd5\u7684\u8fd4\u56de\u503c\u65f6\uff0c\u4ee5\u53ca\u4f7f\u7528Java8\u7684\u5e93\u65b9\u6cd5\u8fd4\u56deOptional\u7684\u60c5\u51b5\u4e0b\uff0c\u4e0d\u7ba1\u662f\u5426\u613f\u610f\uff0c\u90fd\u9700\u8981\u4f7f\u7528Optional\u3002<br \/>\n\u7136\u800c\uff0c\u5728\u521a\u5f00\u59cb\u5b66\u4e60Java8\u65f6\uff0c\u5f88\u5bb9\u6613\u53d1\u73b0\u5f53\u6211\u4eec\u8bd5\u56fe\u81ea\u5df1\u5b9e\u73b0\u65b9\u6cd5\u65f6\uff0c\u5f88\u5c11\u4f1a\u610f\u8bc6\u5230\u201c\u8fd9\u91cc\u5e94\u8be5\u5c06\u8fd4\u56de\u7c7b\u578b\u8bbe\u4e3aOptional\u201d\u3002<\/p>\n<p>\u5047\u8bbe\u6211\u4eec\u521b\u5efa\u4e86\u4e00\u4e2a\u7c7b\u4f3c\u7684\u65b9\u6cd5\uff1a\u201c\u4ece\u7f13\u5b58\u4e2d\u83b7\u53d6\u6c47\u7387\u4fe1\u606f\uff0c\u5982\u679c\u7f13\u5b58\u4e0d\u5b58\u5728\uff0c\u5219\u8fd4\u56de\u9ed8\u8ba4\u503c1\u201d\u3002<\/p>\n<pre class=\"post-pre\"><code>\r\n<span class=\"kd\">public<\/span> <span class=\"nc\">RateInfo<\/span> <span class=\"nf\">getFromCache<\/span><span class=\"o\">(<\/span><span class=\"nc\">String<\/span> <span class=\"n\">fromCurrency<\/span><span class=\"o\">,<\/span> <span class=\"nc\">String<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"c1\">\/\/ \u30ad\u30e3\u30c3\u30b7\u30e5\u306b\u5b58\u5728\u3059\u308c\u3070\u305d\u306eRateInfo\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u3001\u306a\u3051\u308c\u3070null\u3092\u8fd4\u3059<\/span>\r\n<span class=\"o\">}<\/span>\r\n\r\n<span class=\"kd\">public<\/span> <span class=\"nc\">BigDecimal<\/span> <span class=\"nf\">retrieveRate<\/span><span class=\"o\">(<\/span><span class=\"nc\">String<\/span> <span class=\"n\">fromCurrency<\/span><span class=\"o\">,<\/span> <span class=\"nc\">String<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n\r\n    <span class=\"nc\">RateInfo<\/span> <span class=\"n\">rateInfo<\/span> <span class=\"o\">=<\/span> <span class=\"n\">getFromCache<\/span><span class=\"o\">(<\/span><span class=\"n\">fromCurrency<\/span><span class=\"o\">,<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">);<\/span>\r\n\r\n    <span class=\"k\">if<\/span><span class=\"o\">(<\/span><span class=\"n\">rateInfo<\/span> <span class=\"o\">!=<\/span> <span class=\"kc\">null<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n        <span class=\"k\">return<\/span> <span class=\"n\">rateInfo<\/span><span class=\"o\">.<\/span><span class=\"na\">getRate<\/span><span class=\"o\">();<\/span>\r\n    <span class=\"o\">}<\/span>\r\n\r\n    <span class=\"k\">return<\/span> <span class=\"nc\">BigDecimal<\/span><span class=\"o\">.<\/span><span class=\"na\">ONE<\/span><span class=\"o\">;<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u5728\u8fd9\u91cc\uff0cgetFromCache\u65b9\u6cd5\u7684\u884c\u4e3a\u662f\u201c\u5982\u679c\u7f13\u5b58\u4e2d\u5b58\u5728\uff0c\u5219\u8fd4\u56deRateInfo\u5bf9\u8c61\uff1b\u5982\u679c\u4e0d\u5b58\u5728\uff0c\u5219\u8fd4\u56denull\u201d\u3002<br \/>\n\u56e0\u6b64\uff0c\u5728\u8c03\u7528\u5904\u9700\u8981\u8fdb\u884cnull\u68c0\u67e5\u7684if\u8bed\u53e5\u3002<br \/>\n\u6709\u65f6\u5019\u4f1a\u5fd8\u8bb0\u8fdb\u884c\u8fd9\u4e2anull\u68c0\u67e5\uff0c\u5bfc\u81f4\u51fa\u73b0NullPointerException\u7684\u60c5\u51b5\u3002<\/p>\n<p>\u6240\u4ee5\uff0c\u73b0\u5728\u662fOptional\u51fa\u573a\u7684\u65f6\u5019\u4e86\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"kd\">public<\/span> <span class=\"nc\">Optional<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">RateInfo<\/span><span class=\"o\">&gt;<\/span> <span class=\"nf\">getFromCache<\/span><span class=\"o\">(<\/span><span class=\"nc\">String<\/span> <span class=\"n\">fromCurrency<\/span><span class=\"o\">,<\/span> <span class=\"nc\">String<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"c1\">\/\/ \u30ad\u30e3\u30c3\u30b7\u30e5\u304b\u3089RateInfo\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3092\u53d6\u308a\u51fa\u305d\u3046\u3068\u3057\u305f\u7d50\u679c\u3092\u3001Optional&lt;RateInfo&gt;\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u3068\u3057\u3066\u8fd4\u3059<\/span>\r\n<span class=\"o\">}<\/span>\r\n\r\n<span class=\"kd\">public<\/span> <span class=\"nc\">BigDecimal<\/span> <span class=\"nf\">retrieveRate<\/span><span class=\"o\">(<\/span><span class=\"nc\">String<\/span> <span class=\"n\">fromCurrency<\/span><span class=\"o\">,<\/span> <span class=\"nc\">String<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"nc\">Optional<\/span><span class=\"o\">&lt;<\/span><span class=\"nc\">RateInfo<\/span><span class=\"o\">&gt;<\/span> <span class=\"n\">rateInfo<\/span> <span class=\"o\">=<\/span> <span class=\"n\">getFromCache<\/span><span class=\"o\">(<\/span><span class=\"n\">fromCurrency<\/span><span class=\"o\">,<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">);<\/span>\r\n\r\n    <span class=\"k\">return<\/span> <span class=\"n\">rateInfo<\/span><span class=\"o\">.<\/span><span class=\"na\">map<\/span><span class=\"o\">(<\/span><span class=\"nl\">RateInfo:<\/span><span class=\"o\">:<\/span><span class=\"n\">getRate<\/span><span class=\"o\">).<\/span><span class=\"na\">orElse<\/span><span class=\"o\">(<\/span><span class=\"nc\">BigDecimal<\/span><span class=\"o\">.<\/span><span class=\"na\">ONE<\/span><span class=\"o\">);<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u901a\u8fc7\u8fd9\u6837\u505a\uff0c<\/p>\n<ul class=\"post-ul\">\nnull\u30c1\u30a7\u30c3\u30af\u3068\u3044\u3046\u304b\u30aa\u30d6\u30b8\u30a7\u30af\u30c8\u306e\u5b58\u5728\u30c1\u30a7\u30c3\u30af\u3092\u30e1\u30bd\u30c3\u30c9\u306e\u547c\u3073\u5143\u306b\u5f37\u5236\u3067\u304d\u308b<\/p>\n<p>rateInfo.get()\u3067\u30c1\u30a7\u30c3\u30af\u3092\u305b\u305a\u306b\u7121\u7406\u3084\u308a\u5024\u3092\u53d6\u308a\u51fa\u3059\u3053\u3068\u3082\u3067\u304d\u308b\u304c\u3001\u305d\u3046\u3044\u3063\u305f\u30b3\u30fc\u30c9\u306f\u9759\u7684\u89e3\u6790\u3067\u5f3e\u3051\u308b<\/p>\n<p>orElse\u306a\u3069\u306e\u30e1\u30bd\u30c3\u30c9\u3092\u4f7f\u7528\u3059\u308b\u3053\u3068\u3067\u30b3\u30fc\u30c9\u3092\u3059\u3063\u304d\u308a\u66f8\u3051\u308b\n<\/ul>\n<p>\u6709\u8bf8\u591a\u76ca\u5904\u3002<\/p>\n<h1>\u6700\u597d\u907f\u514d\u5f37\u884c\u4f7f\u7528Java8\u7684\u7279\u6027<\/p>\n<p>\u9677\u5165\u7c7b\u4f3c\u4e8e\u6210\u4e3a&#8221;\u4e3a\u4e86\u4f7ffor\u5faa\u73af\u548cnull\u68c0\u67e5\u7edd\u5bf9\u65e0\u6cd5\u901a\u8fc7&#8221;\u7684\u60c5\u51b5\u65f6\u5bb9\u6613\u9677\u5165\u56f0\u5883\u3002\u4e0e\u5176\u4ed6\u8bed\u8a00\u76f8\u6bd4\uff0cJava8\u7684Stream\u548cOptional\u7ecf\u5e38\u5b58\u5728\u4e0d\u597d\u7684\u5730\u65b9\uff0c\u5f53\u6211\u4eec\u5f3a\u884c\u8bd5\u56fe\u89e3\u51b3\u8fd9\u4e9b\u95ee\u9898\u65f6\u53ef\u80fd\u4f1a\u9677\u5165\u56f0\u5883\u3002<\/p>\n<h2>\u4f7f\u7528\u6d41(Stream)\u6765\u66ff\u6362\u5e26\u6709\u7d22\u5f15\u7684for\u5faa\u73af\u3002<\/p>\n<p>\u6bd4\u65b9\u8bf4\uff0c<\/p>\n<pre class=\"post-pre\"><code><span class=\"k\">for<\/span><span class=\"o\">(<\/span><span class=\"kt\">int<\/span> <span class=\"n\">i<\/span><span class=\"o\">=<\/span><span class=\"mi\">0<\/span><span class=\"o\">;<\/span> <span class=\"n\">i<\/span> <span class=\"o\">&lt;<\/span> <span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">size<\/span><span class=\"o\">();<\/span> <span class=\"n\">i<\/span><span class=\"o\">++)<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"nc\">System<\/span><span class=\"o\">.<\/span><span class=\"na\">out<\/span><span class=\"o\">.<\/span><span class=\"na\">println<\/span><span class=\"o\">(<\/span>\r\n        <span class=\"nc\">String<\/span><span class=\"o\">.<\/span><span class=\"na\">valueOf<\/span><span class=\"o\">(<\/span><span class=\"n\">i<\/span><span class=\"o\">)<\/span> <span class=\"o\">+<\/span> <span class=\"s\">\" : \"<\/span> <span class=\"o\">+<\/span> <span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">get<\/span><span class=\"o\">(<\/span><span class=\"n\">i<\/span><span class=\"o\">).<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u6211\u5145\u6ee1\u6597\u5fd7\u5730\u5c1d\u8bd5\u4e86\u4e00\u79cd\u7c7b\u4f3c\u7684\u5904\u7406\u65b9\u5f0f\uff0c\u6ca1\u6709\u4f7f\u7528for\u5faa\u73af\uff0c\u7ed3\u679c\u5374\u5f88\u6210\u529f\uff01<\/p>\n<pre class=\"post-pre\"><code><span class=\"c1\">\/\/ IntStream\u3067\u30eb\u30fc\u30d7\u30ab\u30a6\u30f3\u30bf\u751f\u6210<\/span>\r\n<span class=\"nc\">IntStream<\/span><span class=\"o\">.<\/span><span class=\"na\">range<\/span><span class=\"o\">(<\/span><span class=\"mi\">0<\/span><span class=\"o\">,<\/span> <span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">size<\/span><span class=\"o\">())<\/span>\r\n    <span class=\"o\">.<\/span><span class=\"na\">forEach<\/span><span class=\"o\">(<\/span><span class=\"n\">i<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"nc\">System<\/span><span class=\"o\">.<\/span><span class=\"na\">out<\/span><span class=\"o\">.<\/span><span class=\"na\">println<\/span><span class=\"o\">(<\/span>\r\n        <span class=\"nc\">String<\/span><span class=\"o\">.<\/span><span class=\"na\">valueOf<\/span><span class=\"o\">(<\/span><span class=\"n\">i<\/span><span class=\"o\">)<\/span> <span class=\"o\">+<\/span> <span class=\"s\">\" : \"<\/span> <span class=\"o\">+<\/span> <span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">get<\/span><span class=\"o\">(<\/span><span class=\"n\">i<\/span><span class=\"o\">).<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n\r\n<span class=\"c1\">\/\/ AtomicInteger\u3068forEach\u3067\u9811\u5f35\u308b<\/span>\r\n<span class=\"nc\">AtomicInteger<\/span> <span class=\"n\">i<\/span> <span class=\"o\">=<\/span> <span class=\"k\">new<\/span> <span class=\"nc\">AtomicInteger<\/span><span class=\"o\">();<\/span>\r\n<span class=\"n\">items<\/span><span class=\"o\">.<\/span><span class=\"na\">forEach<\/span><span class=\"o\">(<\/span><span class=\"n\">item<\/span> <span class=\"o\">-&gt;<\/span> <span class=\"nc\">System<\/span><span class=\"o\">.<\/span><span class=\"na\">out<\/span><span class=\"o\">.<\/span><span class=\"na\">println<\/span><span class=\"o\">(<\/span>\r\n        <span class=\"nc\">String<\/span><span class=\"o\">.<\/span><span class=\"na\">valueOf<\/span><span class=\"o\">(<\/span><span class=\"n\">i<\/span><span class=\"o\">.<\/span><span class=\"na\">getAndIncrement<\/span><span class=\"o\">())<\/span> <span class=\"o\">+<\/span> <span class=\"s\">\" : \"<\/span> <span class=\"o\">+<\/span> <span class=\"n\">item<\/span><span class=\"o\">.<\/span><span class=\"na\">getName<\/span><span class=\"o\">());<\/span>\r\n<\/code><\/pre>\n<p>\u5c31\u50cf\u53d8\u6210\u8fd9\u6837\u4e86\u3002<br \/>\n\u524d\u8005\u672c\u6765\u60f3\u8981\u4f5c\u4e3aitems\u7684Stream\u5904\u7406\u8868\u793a\uff0c\u4f46\u662f\u7531\u4e8e\u5728\u7528\u4e8e\u751f\u6210index\u7684IntStream\u4e2d\u4f7f\u7528\u4e86get(i)\u8fdb\u884c\u8bbf\u95ee\uff0c\u6240\u4ee5\u548c\u666e\u901a\u7684for\u5faa\u73af\u5e76\u6ca1\u6709\u533a\u522b\uff0c\u4e5f\u5f88\u96be\u8bfb\u61c2\u3002<br \/>\n\uff08\u4f5c\u8005\u4ee5\u524d\u66fe\u7ecf\u91c7\u7528\u8fc7\u8fd9\u79cd\u5199\u6cd5\uff0c\u4f46\u662f\u56e0\u4e3a\u4e0a\u8ff0\u7684\u7406\u7531\u800c\u505c\u6b62\u4e86\u3002\uff09<\/p>\n<p>\u540e\u8005\u6839\u672c\u5c31\u662f\u80e1\u8bf4\uff0c&#8221;\u4e0d\u80fd\u5728lambda\u5185\u90e8\u9012\u589e\u539f\u59cb\u7c7b\u578bint\uff0c\u6240\u4ee5\u8981\u4f7f\u7528AtomicInteger&#8221;\uff0c\u8fd9\u660e\u663e\u504f\u79bb\u4e86AtomicInteger\u7684\u539f\u672c\u4f7f\u7528\u65b9\u6cd5\uff0c\u6211\u4e0d\u5efa\u8bae\u8fd9\u6837\u505a\u3002<\/p>\n<p>\u5982\u679cJava\u6709\u652f\u6301\u7d22\u5f15\u7684\u96c6\u5408\u64cd\u4f5c\uff08\u4f8b\u5982Kotlin\u7684\u90a3\u6837\uff09\uff0c\u90a3\u5c31\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528\u5b83\uff0c\u4f46\u5f88\u4e0d\u5e78\u76ee\u524d\u8fd8\u6ca1\u6709\u5b9e\u73b0\uff0c\u6240\u4ee5\u6bd4\u8d77\u5f3a\u884c\u4f7f\u7528Stream API\uff0c\u73b0\u9636\u6bb5\u8fd8\u662f\u76f4\u63a5\u4f7f\u7528for\u5faa\u73af\u66f4\u597d\u3002<\/p>\n<h2>\u53ea\u662f\u4e3a\u4e86\u8fdb\u884cnull\u68c0\u67e5\u800c\u521b\u5efaOptional.ofNullable<\/p>\n<p>\u5728\u53e4\u8001\u7684\u5e93\u548cJava7\u4e4b\u524d\u4e5f\u53ef\u4ee5\u4f7f\u7528\u7684\u65b9\u6cd5\u4e2d\uff0c\u6709\u4e9b\u65b9\u6cd5\u53ef\u80fd\u4f1a\u8fd4\u56denull\u4f5c\u4e3a\u8fd4\u56de\u503c\u3002<br \/>\n\u5bf9\u4e8e\u8fd9\u6837\u7684\u65b9\u6cd5\uff0c\u5f53\u53ea\u60f3\u8981&#8221;\u4ec5\u4ec5\u68c0\u67e5\u8fd4\u56de\u503c\u662f\u5426\u4e3anull&#8221;\u65f6\uff0c\u6211\u4eec\u4f1a\u4ea7\u751f\u4e00\u79cd&#8221;\u65e0\u8bba\u5982\u4f55\u4e0d\u8981\u5199if (a != null)\uff01&#8221;\u7684\u60f3\u6cd5\uff0c\u7136\u540e\u5c31\u4f1a\u5199\u51fa\u4e0b\u9762\u8fd9\u6837\u7684\u4ee3\u7801\u3002<\/p>\n<pre class=\"post-pre\"><code>\r\n<span class=\"c1\">\/\/ getText()\u306fnull\u3092\u8fd4\u3057\u5f97\u308b<\/span>\r\n<span class=\"nc\">String<\/span> <span class=\"n\">text<\/span> <span class=\"o\">=<\/span> <span class=\"n\">getText<\/span><span class=\"o\">();<\/span>\r\n\r\n<span class=\"c1\">\/\/ Optional\u3067\u5305\u3093\u3067\u30c1\u30a7\u30c3\u30af\u3002\u4e2d\u8eab\u306e\u5024\u306f\u4f7f\u308f\u306a\u3044<\/span>\r\n<span class=\"k\">if<\/span><span class=\"o\">(<\/span><span class=\"nc\">Optional<\/span><span class=\"o\">.<\/span><span class=\"na\">ofNullable<\/span><span class=\"o\">(<\/span><span class=\"n\">text<\/span><span class=\"o\">).<\/span><span class=\"na\">isPresent<\/span><span class=\"o\">())<\/span> <span class=\"o\">{<\/span>\r\n    <span class=\"k\">return<\/span> <span class=\"s\">\"OK\"<\/span><span class=\"o\">;<\/span>   \r\n<span class=\"o\">}<\/span>\r\n\r\n<span class=\"k\">return<\/span> <span class=\"s\">\"NG\"<\/span><span class=\"o\">;<\/span>\r\n<\/code><\/pre>\n<p>\u4f7f\u7528Optional.isPresent()\u867d\u7136\u4e0d\u592a\u597d\uff0c\u4f46\u76f8\u6bd4\u666e\u901a\u7684\u7a7a\u503c\u68c0\u67e5\uff0c\u4ee3\u7801\u4f1a\u53d8\u5f97\u66f4\u957f\u5e76\u7a0d\u663e\u7e41\u7410\u3002<br \/>\n\u6211\u8ba4\u4e3a\u76f4\u63a5\u4f7f\u7528if(text != null)\u5c31\u53ef\u4ee5\u4e86\u3002<\/p>\n<h3>\u6709\u4e9b\u5730\u65b9\u6b63\u5728\u7169\u60f1\u4e2d-\u50cf\u9ed8\u8a8d\u5f15\u6578\u4e00\u6a23\u4f7f\u7528\u3002<\/p>\n<p>Optional\u4f5c\u4e3a\u4e00\u79cd\u8bbe\u8ba1\u601d\u60f3\uff0c\u4e3b\u8981\u662f\u7528\u4f5c\u201c\u65b9\u6cd5\u8fd4\u56de\u503c\u201d\uff0c\u4e0d\u63a8\u8350\u5c06\u5176\u7528\u4e8e\u5176\u4ed6\u7528\u9014\uff08\u6bd4\u5982\u4f5c\u4e3a\u53c2\u6570\u7684\u7c7b\u578b\uff09\u3002<br \/>\n\uff08\u5f15\u81ear.f stackoverflow &#8211; \u4e3a\u4ec0\u4e48java.util.Optional\u4e0d\u53ef\u5e8f\u5217\u5316\uff0c\u5982\u4f55\u5bf9\u5177\u6709\u8fd9\u79cd\u5b57\u6bb5\u7684\u5bf9\u8c61\u8fdb\u884c\u5e8f\u5217\u5316\uff09<\/p>\n<p>\u867d\u7136\u786e\u5b9e\u53ef\u4ee5\u4f7f\u7528Optional\u7c7b\u578b\u4f5c\u4e3a\u53c2\u6570\uff0c\u4f46\u5982\u679c\u4f20\u5165\u7684Optional\u5bf9\u8c61\u4e3anull\uff0c\u90a3\u4e48\u5c31\u6ca1\u6709\u592a\u591a\u7684\u597d\u5904\u4e86\u3002<br \/>\n\u7136\u800c\uff0c\u5728\u53c2\u6570\u65b9\u9762\uff0c\u6709\u4e00\u79cd\u201c\u53ef\u4ee5\u8fd9\u6837\u4f7f\u7528Optional\u201d\u7684\u65b9\u5f0f\u3002<br \/>\n\u90a3\u5c31\u662f\u50cf\u4f7f\u7528\u9ed8\u8ba4\u53c2\u6570\u4e00\u6837\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"c1\">\/\/ \u5bfe\u8c61\u5546\u54c1\u3092\u6307\u5b9a\u3057\u305f\u901a\u8ca8\u306e\u4fa1\u683c\u306b\u5909\u63db\u3057\u305f\u3082\u306e\u3092\u8fd4\u3059<\/span>\r\n<span class=\"kd\">public<\/span> <span class=\"nc\">Item<\/span> <span class=\"nf\">convert<\/span><span class=\"o\">(<\/span><span class=\"nc\">Item<\/span> <span class=\"n\">item<\/span><span class=\"o\">,<\/span> <span class=\"nc\">String<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n     <span class=\"c1\">\/\/ \u901a\u8ca8\u306e\u6307\u5b9a\u304c\u306a\u3051\u308c\u3070USD\u3092\u4f7f\u7528\u3059\u308b<\/span>\r\n     <span class=\"nc\">String<\/span> <span class=\"n\">currency<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">Optional<\/span><span class=\"o\">.<\/span><span class=\"na\">ofNullable<\/span><span class=\"o\">(<\/span><span class=\"n\">toCurrency<\/span><span class=\"o\">).<\/span><span class=\"na\">orElse<\/span><span class=\"o\">(<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n\r\n     <span class=\"o\">...<\/span>\r\n     <span class=\"o\">...<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<p>\u4e5f\u8bb8\u6709\u50cf\u300c\u4f7f\u7528overload\u300d\u8fd9\u6837\u7684\u89c2\u70b9\uff0c\u4f46\u662f\u5728\u7b2c\u4e09\u65b9\u5e93\u7684\u63a5\u53e3\u5b9e\u73b0\u65b9\u6cd5\u4e2d\u6307\u5b9a\u4e3a\u56de\u8c03\u65b9\u6cd5\u7684\u60c5\u51b5\u4e0b\u65e0\u6cd5\u4f7f\u7528overload\u3002\u6240\u4ee5\u6211\u6b63\u5728\u8003\u8651\u8fd9\u79cd\u7528\u6cd5\u662f\u5426\u53ef\u884c\u3002<\/p>\n<h4>\u5907\u6ce8 (2017\/08\/30)<\/p>\n<p>\u53ef\u80fd\u9700\u8981\u5728\u53e6\u4e00\u4e2a\u65b9\u6cd5\u4e2d\u8fdb\u884c\u76f8\u5e94\u7684\u6539\u8fdb\uff0c\u6b63\u5982\u60a8\u5728\u8bc4\u8bba\u4e2d\u6240\u6307\u51fa\u7684\u3002<\/p>\n<pre class=\"post-pre\"><code><span class=\"c1\">\/\/ \u5bfe\u8c61\u5546\u54c1\u3092\u6307\u5b9a\u3057\u305f\u901a\u8ca8\u306e\u4fa1\u683c\u306b\u5909\u63db\u3057\u305f\u3082\u306e\u3092\u8fd4\u3059<\/span>\r\n<span class=\"kd\">public<\/span> <span class=\"nc\">Item<\/span> <span class=\"nf\">convert<\/span><span class=\"o\">(<\/span><span class=\"nc\">Item<\/span> <span class=\"n\">item<\/span><span class=\"o\">,<\/span> <span class=\"nc\">String<\/span> <span class=\"n\">toCurrency<\/span><span class=\"o\">)<\/span> <span class=\"o\">{<\/span>\r\n     <span class=\"c1\">\/\/ java.util.Objects.toString<\/span>\r\n     <span class=\"nc\">String<\/span> <span class=\"n\">currency1<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">Objects<\/span><span class=\"o\">.<\/span><span class=\"na\">toString<\/span><span class=\"o\">(<\/span><span class=\"n\">toCurrency<\/span><span class=\"o\">,<\/span><span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n\r\n     <span class=\"c1\">\/\/ org.apache.commons.lang3.ObjectUtils.defaultIfNull<\/span>\r\n     <span class=\"nc\">String<\/span> <span class=\"n\">currency2<\/span> <span class=\"o\">=<\/span> <span class=\"nc\">ObjectUtils<\/span><span class=\"o\">.<\/span><span class=\"na\">defaultIfNull<\/span><span class=\"o\">(<\/span><span class=\"n\">toCurrency<\/span><span class=\"o\">,<\/span> <span class=\"s\">\"USD\"<\/span><span class=\"o\">);<\/span>\r\n\r\n     <span class=\"o\">...<\/span>\r\n     <span class=\"o\">...<\/span>\r\n<span class=\"o\">}<\/span>\r\n<\/code><\/pre>\n<h1>\u6700\u7ec8<\/p>\n<ul class=\"post-ul\">\nStream API\u3082Optional\u3082\u3001\u300c\u5358\u306a\u308b\u30e1\u30bd\u30c3\u30c9\u30fb\u30af\u30e9\u30b9\u306e\u8ffd\u52a0\u300d\u3067\u306f\u306a\u304f\u300c\u4eca\u307e\u3067\u3088\u308a\u3082\u52b9\u7387\u7684\u3067\u7406\u89e3\u3057\u3084\u3059\u3044\u66f8\u304d\u65b9\u304c\u3067\u304d\u308b\u300d\u3068\u6349\u3048\u3066\u3001\u8272\u3005\u306a\u66f8\u304d\u65b9\u3092\u63a2\u3063\u3066\u307f\u308b\u3068\u9762\u767d\u3044\u3002<br \/>\n\u3068\u306f\u8a00\u3048\u3001Java8\u6642\u70b9\u3067\u306f\u30a4\u30b1\u3066\u306a\u3044\u90e8\u5206\u3082\u591a\u3044\u306e\u3067\u3001\u76f2\u76ee\u7684\u306b\u4f7f\u7528\u3059\u308b\u306e\u3067\u306f\u306a\u304f\u300c\u4e01\u5ea6\u826f\u3044\u4f7f\u3044\u65b9\u300d\u3092\u63a2\u3063\u3066\u3044\u304f\u306e\u304c\u809d\u8981\u3002\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>\u603b\u7ed3\u4e00\u4e0b(\u4f60\u5728\u8bf4\u4ec0\u4e48\u5462) \u30b3\u30fc\u30c9\u30ec\u30d3\u30e5\u30fc\u3057\u3066\u3044\u308b\u3068\u3001Java8\u306efeature(Stream API\u3068\u304bOpt [&hellip;]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[227],"class_list":["post-31230","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-227"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium 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