{"id":2217,"date":"2018-02-07T16:07:21","date_gmt":"2018-02-07T08:07:21","guid":{"rendered":"https:\/\/ai.zhousir.top\/?p=2217"},"modified":"2018-02-10T13:40:31","modified_gmt":"2018-02-10T05:40:31","slug":"java8-%e6%96%b0%e7%89%b9%e6%80%a7-stream","status":"publish","type":"post","link":"https:\/\/ai.zhousir.top\/?p=2217","title":{"rendered":"Java8-\u65b0\u7279\u6027-Stream"},"content":{"rendered":"
\n

\u4e86\u89e3Stream<\/h3>\n

\u200b Java8\u4e2d\u6709\u4e24\u4e2a\u6700\u4e3a\u91cd\u8981\u7684\u6539\u53d8\uff0c\u4e00\u4e2a\u662fLambda\u8868\u8fbe\u5f0f\uff0c\u53e6\u4e00\u4e2a\u5c31\u662fStream API<\/strong>,\u9488\u5bf9\u5e38\u89c1\u7684\u96c6\u5408\u6570\u636e\u5904\u7406\uff0cStream API \u63d0\u4f9b\u4e86\u4e00\u79cd\u9ad8\u6548\u4e14\u6613\u4e8e\u4f7f\u7528\u7684\u6570\u636e\u5904\u7406\u65b9\u5f0f\u3002<\/p>\n

\u4ec0\u4e48\u662fStream<\/h3>\n

\u57fa\u672c\u6982\u5ff5<\/h4>\n

\u200b \u6d41(Stream)\u7528\u4e8e\u64cd\u4f5c\u6570\u636e\u6e90\u6240\u751f\u6210\u7684\u5143\u7d20\u5e8f\u5217\u3002Java 8\u7ed9Collection\u63a5\u53e3\u589e\u52a0\u4e86\u4e24\u4e2a\u9ed8\u8ba4\u65b9\u6cd5\uff0c\u5b83\u4eec\u53ef\u4ee5\u8fd4\u56de\u4e00\u4e2aStream<\/p>\n

default Stream<E> stream() {
\n\u200b return StreamSupport.stream(spliterator(), false);
\n}\/\/stream()\u8fd4\u56de\u7684\u662f\u4e00\u4e2a\u987a\u5e8f\u6d41<\/p>\n

default Stream<E> parallelStream() {
\n\u200b return StreamSupport.stream(spliterator(), true);
\n}\/\/parallelStream()\u8fd4\u56de\u7684\u662f\u4e00\u4e2a\u5e76\u53d1\u6d41<\/p><\/blockquote>\n

    \n
  1. Stream \u81ea\u5df1\u4e0d\u4f1a\u5b58\u50a8\u5143\u7d20\u3002<\/strong><\/li>\n
  2. Stream \u4e0d\u4f1a\u6539\u53d8\u6e90\u5bf9\u8c61\u3002\u76f8\u53cd\uff0c\u4ed6\u4eec\u4f1a\u8fd4\u56de\u4e00\u4e2a\u6301\u6709\u7ed3\u679c\u7684\u65b0Stream\u3002<\/strong><\/li>\n
  3. Stream \u64cd\u4f5c\u662f\u5ef6\u8fdf\u6267\u884c\u7684\u3002\u8fd9\u610f\u5473\u7740\u4ed6\u4eec\u4f1a\u7b49\u5230\u9700\u8981\u7ed3\u679c\u7684\u65f6\u5019\u624d\u6267\u884c\u3002<\/strong><\/li>\n<\/ol>\n

    \u57fa\u672c\u793a\u4f8b<\/h4>\n

    \u9996\u5148\u8fd9\u91cc\u6709\u4e00\u4e2aEmployee\u7c7b<\/p>\n

    public<\/span> class<\/span> Employee<\/span> <\/span>{\r\n   private<\/span> int<\/span> id;\r\n   private<\/span> String name;\r\n   private<\/span> int<\/span> age;\r\n   private<\/span> double<\/span> salary;\r\n   \/*\u7701\u7565getter setter Constructor*\/<\/span>\r\n}\r\n<\/code><\/pre>\n
    \/\/Employee\u5217\u8868<\/span>\r\nList<Employee> emps = Arrays.asList(\r\n      new<\/span> Employee(102<\/span>, \"\u674e\u56db\"<\/span>, 59<\/span>, 6666.66<\/span>),\r\n      new<\/span> Employee(101<\/span>, \"\u5f20\u4e09\"<\/span>, 18<\/span>, 9999.99<\/span>),\r\n      new<\/span> Employee(103<\/span>, \"\u738b\u4e94\"<\/span>, 28<\/span>, 3333.33<\/span>),\r\n      new<\/span> Employee(104<\/span>, \"\u8d75\u516d\"<\/span>, 20<\/span>, 7777.77<\/span>),\r\n      new<\/span> Employee(104<\/span>, \"\u8d75\u516d\"<\/span>, 19<\/span>, 7777.77<\/span>),\r\n      new<\/span> Employee(104<\/span>, \"\u8d75\u56db\"<\/span>, 40<\/span>, 7777.77<\/span>),\r\n      new<\/span> Employee(105<\/span>, \"\u7530\u4e03\"<\/span>, 38<\/span>, 5555.55<\/span>)\r\n);\r\n<\/code><\/pre>\n
    \u8fd4\u56de\u85aa\u8d44\u5927\u4e8e5000\u7684\u5458\u5de5\u5217\u8868,java8\u4ee5\u524d\u662f\u8fd9\u6837\u505a\u7684<\/p>\n
    List<Employee> newEmps = new<\/span> ArrayList<>();\r\nfor<\/span>(Employee emp : emps){\r\n  if<\/span>(emp.salary > 5000.00<\/span>){\r\n    newEmps.add(emp);\r\n  }\r\n}\r\n<\/code><\/pre>\n
    \u4f7f\u7528Stream API ,\u4ee3\u7801\u53ef\u4ee5\u8fd9\u6837<\/p>\n
    List<Employee> newEmps = emps.stream()\r\n        .filter(s -> s.getSalary() > 5000.00<\/span>)\r\n        .collect(Collectors.toList());\r\n<\/code><\/pre>\n
    \u5148\u901a\u8fc7stream()\u5f97\u5230\u4e00\u4e2aStream\u5bf9\u8c61\uff0c\u7136\u540e\u8c03\u7528Stream\u4e0a\u7684\u65b9\u6cd5\uff0cfilter()\u8fc7\u6ee4\u5f97\u5230\u85aa\u8d44\u5927\u4e8e5000\u7684,\u5b83\u7684\u8fd4\u56de\u503c\u4f9d\u7136\u662f\u4e00\u4e2aStream,\u7136\u540e\u901a\u8fc7\u8c03\u7528collect()\u65b9\u6cd5\u5e76\u4f20\u9012\u4e00\u4e2aCollectors.toList()\u5c06\u7ed3\u679c\u96c6\u5b58\u653e\u5230\u4e00\u4e2aList\u4e2d.<\/p>\n
    \u4f7f\u7528Stream API\u5904\u7406\u96c6\u5408\u7c7b\u4ee3\u7801\u66f4\u52a0\u7b80\u6d01\u6613\u8bfb.<\/p>\n
    \u4e0b\u9762\u4ecb\u7ecd\u4e00\u4e0bStream\u4e2d\u7684\u4e24\u79cd\u64cd\u4f5c<\/p>\n
    Stream\u7684\u4e2d\u95f4\u64cd\u4f5c\u548c\u7ec8\u6b62\u64cd\u4f5c<\/h4>\n
    \u4e2d\u95f4\u64cd\u4f5c<\/strong>:<\/p>\n
    \u200b \u591a\u4e2a \u4e2d\u95f4\u64cd\u4f5c\u53ef\u4ee5\u8fde\u63a5\u8d77\u6765\u5f62\u6210\u4e00\u4e2a \u6d41\u6c34\u7ebf\uff0c\u9664\u975e\u6d41\u6c34\u7ebf\u4e0a\u89e6\u53d1\u7ec8\u6b62\u64cd\u4f5c\uff0c\u5426\u5219 \u4e2d\u95f4\u64cd\u4f5c\u4e0d\u4f1a\u6267\u884c\u4efb\u4f55\u7684 \u5904\u7406\uff01\u800c\u5728 \u7ec8\u6b62\u64cd\u4f5c\u65f6\u4e00\u6b21\u6027\u5168\u90e8 \u5904\u7406\uff0c\u79f0\u4e3a\u201c\u60f0\u6027\u6c42\u503c\u201d<\/p>\n
    \"zhongjianchaoz\"<\/a><\/p>\n
    \u7ec8\u6b62\u64cd\u4f5c<\/strong>:<\/p>\n
    \u200b \u7ec8\u7aef\u64cd\u4f5c\u4f1a\u4ece\u6d41\u7684\u6d41\u6c34\u7ebf\u751f\u6210\u7ed3\u679c\u3002\u5176\u7ed3\u679c\u53ef\u4ee5\u662f\u4efb\u4f55\u4e0d\u662f\u6d41\u7684\u503c\uff0c\u4f8b\u5982\uff1aList\u3001Integer\uff0c\u751a\u81f3\u662f void \u3002<\/p>\n
    \"zhaz\"<\/a><\/p>\n
    \u6536\u96c6<\/strong>\u00a0: collect(Collector c)\u65b9\u6cd5\u9700\u8981\u4e00\u4e2aCollector \u4f5c\u4e3a\u53c2\u6570,Collector \u63a5\u53e3\u4e2d\u65b9\u6cd5\u7684\u5b9e\u73b0\u51b3\u5b9a\u4e86\u5982\u4f55\u5bf9\u6d41\u6267\u884c\u6536\u96c6\u64cd\u4f5c(\u5982\u6536\u96c6\u5230 List\u3001Set\u3001Map)\u3002Java8\u4e2d\u63d0\u4f9b\u4e86\u4e00\u4e2aCollectors\u5de5\u5177\u7c7b, \u5de5\u5177\u4e2d\u63d0\u4f9b\u4e86\u5f88\u591a\u9759\u6001\u65b9\u6cd5\uff0c\u53ef\u4ee5\u65b9\u4fbf\u5730\u521b\u5efa\u5e38\u89c1\u6536\u96c6\u5668\u4f8b<\/p>\n
    \u5177\u4f53\u65b9\u6cd5\u4e0e\u5b9e\u4f8b\u5982\u4e0b\u8868<\/p>\n
    \"sj\"<\/a><\/p>\n
    \u8fd9\u91cc\u53ea\u5217\u51fa\u4e86\u4e00\u4e9b\u5e38\u7528\u7684\u65b9\u6cd5.\u5177\u4f53\u53c2\u8003Java8 Stream API<\/p>\n
    Stream API \u4f7f\u7528<\/h3>\n
    \u4e2d\u95f4\u64cd\u4f5c<\/h4>\n
      \n
    1. \u6620\u5c04(map\/flatMap)
      \n
      map\u2014\u2014\u63a5\u6536 Lambda \uff0c \u5c06\u5143\u7d20\u8f6c\u6362\u6210\u5176\u4ed6\u5f62\u5f0f\u6216\u63d0\u53d6\u4fe1\u606f\u3002\u63a5\u6536\u4e00\u4e2a\u51fd\u6570\u4f5c\u4e3a\u53c2\u6570\uff0c\u8be5\u51fd\u6570\u4f1a\u88ab\u5e94\u7528\u5230\u6bcf\u4e2a\u5143\u7d20\u4e0a\uff0c\u5e76\u5c06\u5176\u6620\u5c04\u6210\u4e00\u4e2a\u65b0\u7684\u5143\u7d20\u3002<\/p>\n
      <R> Stream<R> map(Function<? super T, ? extends R> mapper);<\/code><\/p>\n
      map\u64cd\u4f5c\u4f1a\u5c06\u6d41\u91cc\u7684\u6bcf\u4e2a\u5143\u7d20\u6309mapper\u8f6c\u6362\u540e\u7684\u7ed3\u679c\u6dfb\u52a0\u5230\u4e00\u4e2a\u65b0\u6d41\u4e2d.<\/p><\/blockquote>\n
      List<String> list = Arrays.asList(\"1,2\"<\/span>, \"3,4\"<\/span>);\r\n\/\/\u6bcf\u6b21mapper\u64cd\u4f5c\u8fd4\u56de\u4e00\u4e2a\u6570\u7ec4,\u5c06\u6bcf\u4e2a\u6570\u7ec4\u6dfb\u52a0\u5230\u65b0\u6d41\u4e2d,\u6700\u7ec8\u751f\u6210Stream<String[]><\/span>\r\nStream<String[]> stream = list.stream().map(s -> s.split(\",\"<\/span>));\r\n\/\/\u6bcf\u6b21mapper\u64cd\u4f5c\u8fd4\u56de\u4e00\u4e2a\u6d41Stream<String>,\u5c06\u6bcf\u4e2a\u6d41\u6dfb\u52a0\u5230\u65b0\u6d41\u4e2d,\u6700\u7ec8\u751f\u6210Stream<Stream<String>><\/span>\r\nStream<Stream<String>> streamStream = list.stream().map(s -> Arrays.stream(s.split(\",\"<\/span>)));\r\n<\/code><\/pre>\n
      flatMap\u2014\u2014\u63a5\u6536\u4e00\u4e2a\u51fd\u6570\u4f5c\u4e3a\u53c2\u6570\uff0c\u5c06\u6d41\u4e2d\u7684\u6bcf\u4e2a\u503c\u90fd\u6362\u6210\u53e6\u4e00\u4e2a\u6d41\uff0c\u7136\u540e\u628a\u6240\u6709\u6d41\u8fde\u63a5\u6210\u4e00\u4e2a\u6d41<\/p>\n
      <R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper)<\/code><\/p>\n
      \u5b83\u63a5\u53d7\u4e00\u4e2a\u51fd\u6570mapper\uff0c\u5bf9\u6d41\u4e2d\u7684\u6bcf\u4e00\u4e2a\u5143\u7d20\uff0cmapper\u4f1a\u5c06\u8be5\u5143\u7d20\u8f6c\u6362\u4e3a\u4e00\u4e2a\u6d41Stream\uff0c\u7136\u540e\u628a\u65b0\u751f\u6210\u6d41\u7684\u6bcf\u4e00\u4e2a\u5143\u7d20\u4f20\u9012\u7ed9\u4e0b\u4e00\u4e2a\u64cd\u4f5c.<\/p><\/blockquote>\n
      List<String> list = Arrays.asList(\"1,2\"<\/span>, \"3,4\"<\/span>);\r\n\/\/\u6bcf\u6b21mapper\u64cd\u4f5c\u8fd4\u56de\u4e00\u4e2a\u6d41Stream<String> \u7136\u540e\u5c06\u6d41\u91cc\u7684\u6bcf\u4e2a\u5143\u7d20\u6dfb\u52a0\u5230\u65b0\u6d41\u4e2d,\u6700\u7ec8\u751f\u6210Stream<String><\/span>\r\nStream<String> stringStream = list.stream().flatMap(s -> Arrays.stream(s.split(\",\"<\/span>)));\r\n<\/code><\/pre>\n
      flatMap \u628a Stream \u4e2d\u7684\u5c42\u7ea7\u7ed3\u6784\u6241\u5e73\u5316\uff0c\u5c31\u662f\u5c06\u6700\u5e95\u5c42\u5143\u7d20\u62bd\u51fa\u6765\u653e\u5230\u4e00\u8d77\uff0c\u6700\u7ec8\u751f\u6210\u7684\u65b0 Stream \u91cc\u9762\u90fd\u662f\u76f4\u63a5\u7684\u5b57\u7b26\u4e32\u3002<\/p><\/blockquote>\n<\/li>\n
    2. \u6392\u5e8f(sort)
      \n
      sorted() \u2014\u2014\u81ea\u7136\u6392\u5e8f(\u6839\u636e\u6d41\u4e2d\u5143\u7d20\u5b9e\u73b0\u7684Comparable\u63a5\u53e3\u7684compareTo()\u65b9\u6cd5\u6765\u6392\u5e8f\u7684)<\/p>\n
      sorted(Comparator com) \u2014\u2014\u5b9a\u5236\u6392\u5e8f(\u6839\u636e\u7279\u5b9a\u7684\u6bd4\u8f83\u5668\u6765\u6392\u5e8f)<\/p><\/blockquote>\n
      List<Integer> list = Arrays.asList(1<\/span>,3<\/span>,4<\/span>,0<\/span>,9<\/span>,8<\/span>,5<\/span>);\r\nStream<Integer> sorted = list.stream().sorted();\r\nsorted.forEach(System.out::print);\r\n\/*\r\n \u8f93\u51fa\u7ed3\u679c: 0134589\r\n*\/<\/span>\r\n<\/code><\/pre>\n
      emps.stream()\r\n        .sorted((x, y) -> {\r\n            if<\/span> (x.getAge() == y.getAge()) {\r\n                return<\/span> x.getName().compareTo(y.getName());\r\n            } else<\/span> {\r\n                return<\/span> Integer.compare(x.getAge(), y.getAge());\r\n            }\r\n        }).forEach(System.out::println);\r\n\/*\r\n \u6307\u5b9a\u6bd4\u8f83\u89c4\u5219,\u6309\u59d3\u540d\u6392\u5e8f,\u59d3\u540d\u76f8\u540c\u7684\u518d\u6839\u636e\u5e74\u9f84\u6392\u5e8f\r\n*\/<\/span>\r\n<\/code><\/pre>\n<\/li>\n
    3. \u7b5b\u9009\u4e0e\u5207\u7247
      \n
      filter : \u63a5\u53d7Lambda,\u4ece\u6d41\u4e2d\u6392\u9664\u67d0\u4e9b\u5143\u7d20<\/p>\n
      limit(n) : \u8fd4\u56de\u6d41\u4e2d\u524dn\u4e2a\u5143\u7d20<\/p>\n
      skip(n) : \u8df3\u8fc7\u6d41\u4e2d\u524dn\u4e2a\u5143\u7d20<\/p>\n
      distinct : \u53bb\u6389\u6d41\u4e2d\u91cd\u590d\u5143\u7d20(\u901a\u8fc7hashCode\u548cequles\u65b9\u6cd5\u5224\u65ad\u662f\u5426\u4e3a\u76f8\u540c\u5bf9\u8c61)<\/p><\/blockquote>\n
      filter<\/strong><\/p>\n
      \/\/ \u7b5b\u9009\u51fa\u59d3\u8d75\u7684\u5458\u5de5<\/span>\r\nStream<Employee> resultStream = emps.stream()\r\n        .filter(employee ->\r\n                employee.getName().startsWith(\"\u8d75\"<\/span>));\r\nresultStream.forEach(System.out::println);\r\n\/*\r\n \u8f93\u51fa\u7ed3\u679c:\r\n Employee [id=104, name=\u8d75\u516d, age=20, salary=7777.77]\r\n Employee [id=104, name=\u8d75\u516d, age=19, salary=7777.77]\r\n Employee [id=104, name=\u8d75\u56db, age=40, salary=7777.77]\r\n*\/<\/span>\r\n<\/code><\/pre>\n
      limit<\/strong><\/p>\n
      \/\/\u83b7\u53d6\u5217\u8868\u524d3\u4e2a\u5458\u5de5<\/span>\r\nStream<Employee> limit = emps.stream().limit(3<\/span>);\r\nlimit.forEach(System.out::println);\r\n\/*\r\n Employee [id=102, name=\u674e\u56db, age=59, salary=6666.66]\r\n Employee [id=101, name=\u5f20\u4e09, age=18, salary=9999.99]\r\n Employee [id=103, name=\u738b\u4e94, age=28, salary=3333.33]\r\n*\/<\/span>\r\n<\/code><\/pre>\n
      skin<\/strong><\/p>\n
      \/\/\u53bb\u6389\u524d3\u4e2a\u5458\u5de5<\/span>\r\nStream<Employee> limit = emps.stream().skip(3<\/span>);\r\nlimit.forEach(System.out::println);\r\n\/*\r\n Employee [id=104, name=\u8d75\u516d, age=20, salary=7777.77]\r\n Employee [id=104, name=\u8d75\u516d, age=19, salary=7777.77]\r\n Employee [id=104, name=\u8d75\u56db, age=40, salary=7777.77]\r\n Employee [id=105, name=\u7530\u4e03, age=38, salary=5555.55]\r\n*\/<\/span>\r\n<\/code><\/pre>\n
      distinct<\/strong><\/p>\n
      List<Integer> list = Arrays.asList(1<\/span>, 1<\/span>, 2<\/span>, 2<\/span>, 3<\/span>, 3<\/span>, 3<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>);\r\nStream<Integer> distinct = list.stream().distinct();\/\/\u53bb\u6389\u91cd\u590d\u5143\u7d20<\/span>\r\ndistinct.forEach(System.out::print);\r\n\/*\r\n 123456\r\n*\/<\/span>\r\n<\/code><\/pre>\n<\/li>\n<\/ol>\n
      \u7ec8\u6b62\u64cd\u4f5c<\/h4>\n
        \n
      1. \u67e5\u627e\u4e0e\u5339\u914d<\/li>\n<\/ol>\n
        allMatch\u2014\u2014\u68c0\u67e5\u662f\u5426\u5339\u914d\u6240\u6709\u5143\u7d20
        \nanyMatch\u2014\u2014\u68c0\u67e5\u662f\u5426\u81f3\u5c11\u5339\u914d\u4e00\u4e2a\u5143\u7d20
        \nnoneMatch\u2014\u2014\u68c0\u67e5\u662f\u5426\u6ca1\u6709\u5339\u914d\u7684\u5143\u7d20
        \nfindFirst\u2014\u2014\u8fd4\u56de\u7b2c\u4e00\u4e2a\u5143\u7d20
        \nfindAny\u2014\u2014\u8fd4\u56de\u5f53\u524d\u6d41\u4e2d\u7684\u4efb\u610f\u5143\u7d20
        \ncount\u2014\u2014\u8fd4\u56de\u6d41\u4e2d\u5143\u7d20\u7684\u603b\u4e2a\u6570
        \nmax\u2014\u2014\u8fd4\u56de\u6d41\u4e2d\u6700\u5927\u503c
        \nmin\u2014\u2014\u8fd4\u56de\u6d41\u4e2d\u6700\u5c0f\u503c<\/p><\/blockquote>\n
        allMatch<\/strong><\/p>\n
        List<Integer> list = Arrays.asList(1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>);\r\nboolean<\/span> b = list.stream().allMatch(i -> i < 10<\/span>);\/\/\u68c0\u67e5\u6240\u6709\u5143\u7d20\u662f\u5426\u90fd\u5c0f\u4e8e10<\/span>\r\n\/\/true<\/span>\r\n<\/code><\/pre>\n
        anyMatch<\/strong><\/p>\n
        List<Integer> list = Arrays.asList(1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>);\r\nboolean<\/span> b = list.stream().anyMatch(i -> i < 2<\/span>);\/\/\u68c0\u67e5\u662f\u5426\u81f3\u5c11\u6709\u4e00\u4e2a\u5143\u7d20\u5c0f\u4e8e2<\/span>\r\n\/\/true<\/span>\r\n<\/code><\/pre>\n
        noneMatch<\/strong><\/p>\n
        List<Integer> list = Arrays.asList(1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>);\r\nboolean<\/span> b = list.stream().noneMatch(i -> i < 2<\/span>);\/\/\u68c0\u67e5\u662f\u5426\u6ca1\u6709\u4e00\u4e2a\u5143\u7d20\u5c0f\u4e8e2<\/span>\r\n\/\/false<\/span>\r\n<\/code><\/pre>\n
        findFirst<\/strong><\/p>\n
        \/\/\u8fd4\u56delist\u7b2c\u4e00\u4e2a\u5143\u7d20<\/span>\r\nOptional<Integer> any = list.stream().findFirst();\r\nSystem.out.println(any.get());\r\n<\/code><\/pre>\n
        Optional<T><\/code> \u7c7b\u662f\u4e00\u4e2a\u662f\u4e00\u4e2a\u5bb9\u5668\u7c7b,\u4ee3\u8868\u4e00\u4e2a\u503c\u5b58\u5728\u6216\u4e0d\u5b58\u5728,\u539f\u6765\u7528 null \u8868\u793a\u4e00\u4e2a\u503c\u4e0d\u5b58\u5728,\u73b0\u5728Optional<T><\/code>\u53ef\u4ee5\u66f4\u597d\u7684\u8868\u8fbe\u8fd9\u4e2a\u6982\u5ff5,\u5e76\u4e14\u53ef\u4ee5\u907f\u514d\u7a7a\u6307\u9488\u5f02\u5e38<\/p>\n
        \u8fd9\u91ccfindFirst()\u67e5\u627e\u7b2c\u4e00\u4e2a\u5143\u7d20\u6709\u53ef\u80fd\u4e3a\u7a7a,\u5c31\u628a\u7ed3\u679c\u5c01\u88c5\u6210\u4e00\u4e2aOptional\u7c7b.<\/p><\/blockquote>\n
        List<Integer> list = Arrays.asList(1<\/span>, 2<\/span>, 3<\/span>, 4<\/span>, 5<\/span>, 6<\/span>);\r\nlong<\/span> count = list.stream().count();\/\/\u7edf\u8ba1\u5143\u7d20\u4e2a\u6570<\/span>\r\nSystem.out.println(count);\/\/6<\/span>\r\nOptional<Integer> max = list.stream().max(Integer::compareTo);\/\/\u6700\u5927\u503c<\/span>\r\nSystem.out.println(max.get());\/\/6<\/span>\r\nOptional<Integer> min = list.stream().min(Integer::compareTo);\/\/\u6700\u5c0f\u503c<\/span>\r\nSystem.out.println(min.get());\/\/1<\/span>\r\n<\/code><\/pre>\n
          \n
        1. \u89c4\u7ea6(reduce)
          \n
          `reduce(T identity, BinaryOperator bo) \/ reduce(BinaryOperator) \u2014\u2014\u53ef\u4ee5\u5c06\u6d41\u4e2d\u5143\u7d20\u6309\u7167\u6307\u5b9a\u7684\u4e8c\u9662\u8fd0\u7b97\u53cd\u590d\u7ed3\u5408\u8d77\u6765\uff0c\u5f97\u5230\u4e00\u4e2a\u503c<\/p>\n
          identity : \u8d77\u59cb\u503c<\/p>\n
          BinaryOperator : \u4e8c\u5143\u8fd0\u7b97<\/p><\/blockquote>\n
          List<Integer> list = Arrays.asList(1<\/span>,2<\/span>,3<\/span>,4<\/span>,5<\/span>,6<\/span>,7<\/span>,8<\/span>,9<\/span>,10<\/span>);\r\nInteger sum = list.stream()\r\n   .reduce(0<\/span>, (x, y) -> x + y);\r\nSystem.out.println(sum);\r\n\/*\r\n \u8f93\u51fa\u7ed3\u679c 55\r\n*\/<\/span>\r\n<\/code><\/pre>\n
          \u8fd9\u91ccreduce\u64cd\u4f5c\u4e2d,\u8d77\u59cb\u503c\u4e3a0,\u7b2c\u4e00\u6b21x\u4e3a0,list\u4e2d\u7b2c\u4e00\u4e2a\u5143\u7d201\u4e3ay \u7ecf\u884c(x+y)\u64cd\u4f5c,\u7136\u540e\u53c8\u628a(x+y)\u7684\u503c\u4f5c\u4e3ax, list\u4e2d\u7b2c\u4e8c\u4e2a\u5143\u7d202\u4f5c\u4e3ay,\u4f9d\u6b21\u7d2f\u52a0.\u6700\u7ec8\u5f97\u5230\u4e00\u4e2asum\u503c<\/p>\n
          Optional<Double> op = emps.stream()\r\n   .map(Employee::getSalary)\r\n   .reduce(Double::sum);\/\/\u8ba1\u7b97\u6240\u6709\u5458\u5de5\u85aa\u8d44\u603b\u548c<\/span>\r\nSystem.out.println(op.get());\r\n<\/code><\/pre>\n
          \u8fd9\u4e2a\u5730\u65b9\u7531\u4e8e\u6ca1\u6709\u521d\u59cb\u503c,\u8ba1\u7b97\u7ed3\u679c\u53ef\u80fd\u4e3a\u7a7a(\u5217\u8868\u4e3a\u7a7a\u7684\u60c5\u51b5),\u6240\u4ee5\u5c31\u628a\u8ba1\u7b97\u7ed3\u679c\u5c01\u88c5\u5230Optional\u4e2d\u907f\u514d\u7a7a\u6307\u9488\u5f02\u5e38<\/p><\/blockquote>\n<\/li>\n
        2. \u6536\u96c6(collect)<\/li>\n<\/ol>\n
          collect\u2014\u2014\u5c06\u6d41\u8f6c\u6362\u4e3a\u5176\u4ed6\u5f62\u5f0f\u3002\u63a5\u6536\u4e00\u4e2a Collector\u63a5\u53e3\u7684\u5b9e\u73b0\uff0c\u7528\u4e8e\u7ed9Stream\u4e2d\u5143\u7d20\u505a\u6c47\u603b\u7684\u65b9\u6cd5<\/p>\n
          <R, A> R collect(Collector<? super T, A, R> collector);<\/code><\/p><\/blockquote>\n
          \/\/\u6536\u96c6\u5458\u5de5\u59d3\u540d\u5230List\u96c6\u5408<\/span>\r\nList<String> list = emps.stream()\r\n   .map(Employee::getName)\r\n   .collect(Collectors.toList());\r\nlist.forEach(System.out::print);\r\n\/\/ \u8f93\u51fa: \u674e\u56db\u5f20\u4e09\u738b\u4e94\u8d75\u516d\u8d75\u516d\u8d75\u516d\u7530\u4e03<\/span>\r\n<\/code><\/pre>\n
          \/\/\u6536\u96c6\u5458\u5de5\u59d3\u540d\u5230Set\u96c6\u5408<\/span>\r\nSet<String> set = emps.stream()\r\n   .map(Employee::getName)\r\n   .collect(Collectors.toSet());\r\nset.forEach(System.out::println);\r\n\/\/ \u8f93\u51fa : \u674e\u56db\u5f20\u4e09\u738b\u4e94\u8d75\u516d\u7530\u4e03<\/span>\r\n\/\/------------------------------------<\/span>\r\nHashSet<String> hs = emps.stream()\r\n    .map(Employee::getName)\r\n    .collect(Collectors.toCollection(HashSet::new<\/span>));\r\nhs.forEach(System.out::println);\r\n\/\/ \u8f93\u51fa : \u674e\u56db\u5f20\u4e09\u738b\u4e94\u8d75\u516d\u7530\u4e03<\/span>\r\n<\/code><\/pre>\n
            \n
          1. \u5206\u7ec4<\/li>\n<\/ol>\n
            groupingBy : \u6839\u636e\u6307\u5b9a\u7684\u5143\u7d20\u5bf9\u6d41\u4e2d\u6570\u636e\u8fdb\u884c\u5206\u7ec4<\/p><\/blockquote>\n
            \/\/\u6309\u7167\u5458\u5de5\u59d3\u6c0f\u5206\u7ec4,\u8fd9\u91cc\u4e0d\u8003\u8651\u590d\u59d3<\/span>\r\nMap<String, List<Employee>> collect = emps.stream()\r\n        .collect(Collectors\r\n                .groupingBy(emp -> String.valueOf(emp.getName().charAt(0<\/span>))));\r\ncollect.forEach((k, v) -> {\r\n    System.out.println(k + \":\"<\/span> + v);\r\n});\r\n<\/code><\/pre>\n
            \u8f93\u51fa\u7ed3\u679c\u4e3a:<\/p>\n
            \u7530:[Employee [id=105, name=\u7530\u4e03, age=38, salary=5555.55]<\/p>\n
            \u5f20:[Employee [id=101, name=\u5f20\u4e09, age=18, salary=9999.99]<\/p>\n
            \u8d75:[Employee [id=104, name=\u8d75\u516d, age=20, salary=7777.77],<\/p>\n
            \u200b Employee [id=104, name=\u8d75\u516d, age=19, salary=7777.77],<\/p>\n
            \u200b Employee [id=104, name=\u8d75\u56db, age=40, salary=7777.77]]<\/p>\n
            \u738b:[Employee [id=103, name=\u738b\u4e94, age=28, salary=3333.33]
            \n\u674e:[Employee [id=102, name=\u674e\u56db, age=59, salary=6666.66]<\/p><\/blockquote>\n
              \n
            1. \u5206\u533a<\/li>\n<\/ol>\n
              partitioningBy : \u6309\u7167\u7ed9\u5b9a\u6761\u4ef6\u5bf9\u6d41\u4e2d\u5143\u7d20\u8fdb\u884c\u5206\u533a<\/p><\/blockquote>\n
              \/\/\u5c06\u5458\u5de5\u4ee5\u85aa\u8d446000.00\u4e3a\u754c\u9650\u5206\u533a<\/span>\r\nMap<Boolean, List<Employee>> collect = emps.stream()\r\n        .collect(Collectors.partitioningBy(e -> e.getSalary() > 6000.00<\/span>));\r\ncollect.forEach((k, v) -> {\r\n    System.out.println(k + \":\"<\/span> + v);\r\n});\r\n<\/code><\/pre>\n
              \u8f93\u51fa\u7ed3\u679c\u4e3a:<\/p>\n
              false:[Employee [id=103, name=\u738b\u4e94, age=28, salary=3333.33],<\/p>\n
              \u200b Employee [id=105, name=\u7530\u4e03, age=38, salary=5555.55]]<\/p>\n
              true:[Employee [id=102, name=\u674e\u56db, age=59, salary=6666.66],<\/p>\n
              \u200b Employee [id=101, name=\u5f20\u4e09, age=18, salary=9999.99],<\/p>\n
              \u200b Employee [id=104, name=\u8d75\u516d, age=20, salary=7777.77],<\/p>\n
              \u200b Employee [id=104, name=\u8d75\u516d, age=19, salary=7777.77],<\/p>\n
              \u200b Employee [id=104, name=\u8d75\u56db, age=40, salary=7777.77]]<\/p><\/blockquote>\n
              Optional \u7c7b<\/h3>\n
              \u4ecb\u7ecd<\/h4>\n
              Optional \u5bb9\u5668\u7c7b\uff1a\u7528\u4e8e\u5c3d\u91cf\u907f\u514d\u7a7a\u6307\u9488\u5f02\u5e38<\/p><\/blockquote>\n
              \u65b9\u6cd5<\/strong><\/p>\n
              Optional \u5bb9\u5668\u7c7b\uff1a\u7528\u4e8e\u5c3d\u91cf\u907f\u514d\u7a7a\u6307\u9488\u5f02\u5e38<\/p>\n
              Optional.of(T t) : \u521b\u5efa\u4e00\u4e2a Optional \u5b9e\u4f8b<\/p>\n
              Optional.empty() : \u521b\u5efa\u4e00\u4e2a\u7a7a\u7684 Optional \u5b9e\u4f8b<\/p>\n
              Optional.ofNullable(T t):\u82e5 t \u4e0d\u4e3a null,\u521b\u5efa Optional \u5b9e\u4f8b,\u5426\u5219\u521b\u5efa\u7a7a\u5b9e\u4f8b<\/p>\n
              isPresent() : \u5224\u65ad\u662f\u5426\u5305\u542b\u503c<\/p>\n
              orElse(T t) : \u5982\u679c\u8c03\u7528\u5bf9\u8c61\u5305\u542b\u503c\uff0c\u8fd4\u56de\u8be5\u503c\uff0c\u5426\u5219\u8fd4\u56det<\/p>\n
              orElseGet(Supplier s) :\u5982\u679c\u8c03\u7528\u5bf9\u8c61\u5305\u542b\u503c\uff0c\u8fd4\u56de\u8be5\u503c\uff0c\u5426\u5219\u8fd4\u56de s \u83b7\u53d6\u7684\u503c<\/p>\n
              map(Function f): \u5982\u679c\u6709\u503c\u5bf9\u5176\u5904\u7406\uff0c\u5e76\u8fd4\u56de\u5904\u7406\u540e\u7684Optional\uff0c\u5426\u5219\u8fd4\u56de Optional.empty()<\/p>\n
              flatMap(Function mapper):\u4e0e map \u7c7b\u4f3c\uff0c\u8981\u6c42\u8fd4\u56de\u503c\u5fc5\u987b\u662fOptional<\/p><\/blockquote>\n
              \u5c0f\u7ed3<\/h3>\n
              Stream \u662f Java8 \u4e2d\u5904\u7406\u96c6\u5408\u7684\u5173\u952e\u62bd\u8c61\u6982\u5ff5\uff0c\u5b83\u53ef\u4ee5\u6307\u5b9a\u4f60\u5e0c\u671b\u5bf9\u96c6\u5408\u8fdb\u884c\u7684\u64cd\u4f5c\uff0c\u53ef\u4ee5\u6267\u884c\u975e\u5e38\u590d\u6742\u7684\u67e5\u627e\u3001\u8fc7\u6ee4\u548c\u6620\u5c04\u6570\u636e\u7b49\u64cd\u4f5c\u3002\u4f7f\u7528Stream API \u5bf9\u96c6\u5408\u6570\u636e\u8fdb\u884c\u64cd\u4f5c\uff0c\u5c31\u7c7b\u4f3c\u4e8e\u4f7f\u7528 SQL \u6267\u884c\u7684\u6570\u636e\u5e93\u67e5\u8be2\u3002\u4e5f\u53ef\u4ee5\u4f7f\u7528 Stream API \u6765\u5e76\u884c\u6267\u884c\u64cd\u4f5c\u3002<\/p>\n
              \u7b80\u800c\u8a00\u4e4b\uff0cStream API \u63d0\u4f9b\u4e86\u4e00\u79cd\u9ad8\u6548\u4e14\u6613\u4e8e\u4f7f\u7528\u7684\u5904\u7406\u6570\u636e\u7684\u65b9\u5f0f<\/p><\/blockquote>\n
              \u539f\u6587\u94fe\u63a5 : Java8-\u65b0\u7279\u6027-Stream | \u706b\u5c27<\/a><\/p>\n<\/div>\n
               <\/p>\n","protected":false},"excerpt":{"rendered":"
              \u4e86\u89e3Stream \u200b Java8\u4e2d\u6709\u4e24\u4e2a\u6700\u4e3a\u91cd\u8981\u7684\u6539\u53d8\uff0c\u4e00\u4e2a\u662fLambda\u8868\u8fbe\u5f0f\uff0c\u53e6\u4e00\u4e2a\u5c31\u662fStream AP […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[103],"tags":[],"_links":{"self":[{"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=\/wp\/v2\/posts\/2217"}],"collection":[{"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2217"}],"version-history":[{"count":3,"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=\/wp\/v2\/posts\/2217\/revisions"}],"predecessor-version":[{"id":2223,"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=\/wp\/v2\/posts\/2217\/revisions\/2223"}],"wp:attachment":[{"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2217"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2217"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/ai.zhousir.top\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2217"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}