{"id":69,"date":"2014-08-05T11:24:42","date_gmt":"2014-08-05T03:24:42","guid":{"rendered":"http:\/\/www.espandy.com\/?p=69"},"modified":"2014-08-05T11:24:42","modified_gmt":"2014-08-05T03:24:42","slug":"jdk8%e6%96%b0%e7%89%b9%e6%80%a7-%e4%ba%ae%e7%9e%8e%e7%9c%bc%e7%9a%84lambda%e8%a1%a8%e8%be%be%e5%bc%8f","status":"publish","type":"post","link":"https:\/\/www.espandy.com\/?p=69","title":{"rendered":"jdk8\u65b0\u7279\u6027-\u4eae\u778e\u773c\u7684lambda\u8868\u8fbe\u5f0f"},"content":{"rendered":"
\n

\u53c2\u8003\uff1a
\nhttp:\/\/www.oracle.com\/technetwork\/articles\/java\/architect-lambdas-part1-2080972.html
\nhttp:\/\/www.oracle.com\/technetwork\/articles\/java\/architect-lambdas-part2-2081439.html
\nhttp:\/\/blog.csdn.net\/goldenfish1919\/article\/details\/22747375<\/p>\n

\n

jdk8\u4e4b\u524d\uff0c\u5c24\u5176\u662f\u5728\u5199GUI\u7a0b\u5e8f\u7684\u4e8b\u4ef6\u76d1\u542c\u7684\u65f6\u5019\uff0c\u5404\u79cd\u7684\u533f\u540d\u5185\u90e8\u7c7b\uff0c\u5927\u628a\u5927\u628a\u62d6\u6c93\u7684\u4ee3\u7801\uff0c\u7a0b\u5e8f\u6beb\u65e0\u7f8e\u611f\u53ef\u8a00\uff01\u65e2\u7136java\u4e2d\u4e00\u5207\u7686\u4e3a\u5bf9\u8c61\uff0c\u90a3\u4e48\uff0c\u5c31\u7c7b\u4f3c\u4e8e\u67d0\u4e9b\u52a8\u6001\u8bed\u8a00\u4e00\u6837\uff0c\u51fd\u6570\u4e5f\u53ef\u4ee5\u5f53\u6210\u662f\u5bf9\u8c61\u554a\uff01\u4ee3\u7801\u5757\u4e5f\u53ef\u4ee5\u5f53\u6210\u662f\u5bf9\u8c61\u554a\uff01\u968f\u7740\u51fd\u6570\u5f0f\u7f16\u7a0b\u7684\u6982\u5ff5\u8d8a\u6765\u8d8a\u6df1\u5165\u4eba\u5fc3\uff0cjava\u4e2dCODE=OBJECT\u7684\u8fd9\u4e00\u5929\u7ec8\u4e8e\u5230\u6765\u4e86\uff01\u5982\u679c\u4f60\u8ba4\u4e3alambda\u8868\u8fbe\u5f0f\u4ec5\u4ec5\u662f\u4e3a\u4e86\u4ece\u8bed\u6cd5\u4e0a\u7b80\u5316\u533f\u540d\u5185\u90e8\u7c7b\uff0c\u90a3\u5c31\u592a\u5c0f\u770bjdk8\u7684lambda\u4e86\uff01<\/p>\n

\u4e0b\u9762\u6211\u4eec\u5c31\u6765\u770b\u4e0blambda\u8868\u8fbe\u5f0f\u662f\u5982\u4f55\u4eae\u778e\u4f60\u7684\u773c\u7684\uff01<\/p>\n

lambda\u7684\u5b9a\u4e49
\nFunda-men-tally, a lambda expression is just a shorter way of writing an implementation of a method for later execution.
\n\uff081\uff09lambda\u662f\u65b9\u6cd5\u7684\u5b9e\u73b0
\n\uff082\uff09lambda\u662f\u5ef6\u8fdf\u6267\u884c\u7684
\n\u9996\u5148\u770b\u4e00\u4e2a\u7528\u533f\u540d\u5185\u90e8\u7c7b\u7684\u4f8b\u5b50\uff1a<\/p>\n


public class Test1{\n  public static void main(String args[]){\n    Runnable r = new Runnable(){\n      public void run(){\n        System.out.println(\"hello,lambda!\");\n      }\n    };\n    r.run();\n  }\n}\n<\/code><\/pre>\n
\u8981\u6362\u6210lambda\u662f\u4ec0\u4e48\u6837\u7684\u5462\uff1f<\/p>\n

public class Test2{\n        public static void main(String args[]){\n                Runnable r = ()->System.out.println(\"hello,lambda\");\n                r.run();\n        }\n}\n<\/code><\/pre>\n
\u539f\u5148\u89815\u884c\u4ee3\u7801\uff0c\u73b0\u5728\u6362\u6210\u4e86\u4ec5\u4ec51\u884c\uff01
\n\u8fd9\u4ed6\u5988\u7684\u5f97\u7701\u591a\u5c11\u4ee3\u7801\u554a\uff01
\n\u6709\u6728\u6709\u5f88\u5174\u594b\u554a\uff01
\n\u4e0b\u9762\u8fd8\u6709\u66f4\u523a\u6fc0\u7684\uff01
\nlambda\u662f\u5982\u4f55\u505a\u5230\u7684\u5462\uff1f\u770b\u4e00\u4e0b\u53cd\u7f16\u8bd1\u4e4b\u540e\u7684\u5b57\u8282\u7801\uff1a<\/p>\n

public static void main(java.lang.String[]);\n   descriptor: ([Ljava\/lang\/String;)V\n   flags: ACC_PUBLIC, ACC_STATIC\n   Code:\n    stack=1, locals=2, args_size=1\n      0: invokedynamic #2,  0                 \/\/ InvokeDynamic #0:run:()Ljava\/lang\/Runnable;\n      5: astore_1       \n      6: aload_1         \n      7: invokeinterface #3,  1             \/\/ InterfaceMethod java\/lang\/Runnable.run:()V\n      12: return          \n    LineNumberTable:\n      line 3: 0\n      line 4: 6\n      line 5: 12\n}\n<\/code><\/pre>\n
\u6ce8\u610f\uff1a<\/strong>\u4e0a\u9762\u6709\u4e00\u4e2a\u53eb\u505ainvokedynamic\u7684\u6307\u4ee4\u3002invokedynamic\u662f\u4ecejdk7\u5f00\u59cb\u5f15\u5165\u7684\uff0cjdk8\u5f00\u59cb\u843d\u5730\u3002
\n\u53ef\u4ee5\u770b\u51fa\u6765lambda\u5e76\u4e0d\u662f\u8bed\u6cd5\u7cd6\uff0c\u5b83\u4e0d\u662f\u50cf\u533f\u540d\u5185\u90e8\u7c7b\u90a3\u6837\u751f\u6210\u90a3\u79cd\u5e26\u6709$\u7684\u533f\u540d\u7c7b\u3002
\n\u7b80\u5355\u7684\u8bf4\uff0c\u8fd9\u91cc\u53ea\u662f\u5b9a\u4e49\u4e86\u4e00\u4e2a\u65b9\u6cd5\u8c03\u7528\u70b9\uff0c\u5177\u4f53\u8c03\u7528\u90a3\u4e2a\u65b9\u6cd5\u8981\u5230\u8fd0\u884c\u65f6\u624d\u80fd\u51b3\u5b9a\uff0c\u8fd9\u5c31\u662f\u524d\u9762\u6240\u8bf4\u7684\uff1a\u5ef6\u8fdf\u6267\u884c\u3002
\n\u5177\u4f53\u7684\u7ec6\u8282\u8bf7google\uff1ainvokedynamic\u3002<\/p>\n
\n
\u4e3a\u4e86\u914d\u5408lambda\uff0cjdk8\u5f15\u5165\u4e86\u4e00\u4e2a\u65b0\u7684\u5b9a\u4e49\u53eb\u505a\uff1a\u51fd\u6570\u5f0f\u63a5\u53e3\uff08Functional interfaces\uff09
\n\u51fd\u6570\u5f0f\u63a5\u53e3\uff1a
\nit is an interface that requires exactly one method to be implemented in order to satisfy the requirements of the interface.
\n\uff081\uff09\u662f\u4e00\u4e2a\u63a5\u53e3
\n\uff082\uff09\u53ea\u6709\u4e00\u4e2a\u5f85\u5b9e\u73b0\u7684\u65b9\u6cd5
\n\u56e0\u4e3ajdk8\u5f00\u59cb\uff0c\u63a5\u53e3\u53ef\u4ee5\u6709default\u65b9\u6cd5\uff0c\u6240\u4ee5\uff0c\u51fd\u6570\u5f0f\u63a5\u53e3\u4e5f\u662f\u53ef\u4ee5\u6709default\u65b9\u6cd5\u7684\uff0c\u4f46\u662f\uff0c\u53ea\u80fd\u6709\u4e00\u4e2a\u672a\u5b9e\u73b0\u7684\u65b9\u6cd5\u3002
\n\u4e0e\u6b64\u5bf9\u5e94\uff0c\u65b0\u5f15\u5165\u4e86\u4e00\u4e2a\u6ce8\u89e3\uff1a @FunctionalInterface
\n\u8fd9\u4e2a\u6ce8\u89e3\u53ea\u662f\u8d77\u6587\u6863\u7684\u4f5c\u7528\uff0c\u8bf4\u660e\u8fd9\u4e2a\u63a5\u53e3\u662f\u51fd\u6570\u5f0f\u63a5\u53e3\uff0c\u7f16\u8bd1\u5668\u5e76\u4e0d\u4f1a\u4f7f\u7528\u8fd9\u4e2a\u6ce8\u89e3\u6765\u51b3\u5b9a\u4e00\u4e2a\u63a5\u53e3\u662f\u4e0d\u662f\u51fd\u6570\u5f0f\u63a5\u53e3\u3002
\n\u4e0d\u7ba1\u52a0\u4e0d\u52a0@FunctionalInterface\u8fd9\u4e2a\u6ce8\u89e3\uff0c\u4e0b\u9762\u7684\u63a5\u53e3\u90fd\u662f\u51fd\u6570\u5f0f\u63a5\u53e3\uff1a<\/p>\n

interface Something { \n  public String doit(Integer i); \n} \n<\/code><\/pre>\n
lambda\u7684\u8bed\u6cd5
\nA lambda in Java essentially consists of three parts: a parenthesized set of parameters, an arrow, and then a body,
\nwhich can either be a single expression or a block of Java code.
\nlambda\u5305\u542b3\u4e2a\u90e8\u5206\uff1a
\n– \uff081\uff09\u62ec\u5f27\u5305\u8d77\u6765\u7684\u53c2\u6570
\n– \uff082\uff09\u4e00\u4e2a\u7bad\u5934
\n– \uff083\uff09\u65b9\u6cd5\u4f53\uff0c\u53ef\u4ee5\u662f\u5355\u4e2a\u8bed\u53e5\uff0c\u4e5f\u53ef\u4ee5\u662f\u8bed\u53e5\u5757
\n\u53c2\u6570\u53ef\u4ee5\u5199\u7c7b\u578b\uff0c\u4e5f\u53ef\u4ee5\u4e0d\u5199\uff0cjvm\u5f88\u667a\u80fd\u7684\uff0c\u5b83\u80fd\u81ea\u5df1\u63a8\u7b97\u51fa\u6765
\npublic class Test3{
\n        public static void main(String… args) {
\n            Comparator c = (String lhs, String rhs) -> lhs.compareTo(rhs);
\n            int result = c.compare(“Hello”, “World”);
\n                System.out.println(result);
\n        }
\n}
\n\u65b9\u6cd5\u53ef\u4ee5\u6709\u8fd4\u56de\uff0c\u4e5f\u53ef\u4ee5\u65e0\u8fd4\u56de\uff0c\u5982\u679c\u6709\u591a\u4e2a\u8bed\u53e5\uff0c\u8fd8\u8981\u8fd4\u56de\u503c\uff0c\u9700\u8981\u52a0\u4e0areturn
\npublic class Test4{
\n    public static void main(String… args) {
\n      Comparator<\/string> c =(lhs, rhs) ->{
\n            System.out.println(“I am comparing ” +lhs + ” to ” + rhs);
\n              return lhs.compareTo(rhs);
\n        };
\n        int result = c.compare(“Hello”, “World”);
\n        System.out.println(result);
\n    }
\n}
\n\u4e00\u4e2a\u5f88\u6709\u610f\u601d\u7684\u4e8b\u60c5\uff1a
\n\u4e4b\u524d\u6211\u4eec\u8bf4Object\u662f\u4e00\u5207\u7c7b\u7684\u7236\u7c7b\uff0c\u7136\u800c\u5728\u52a0\u5165\u4e86lambda\u4ee5\u540e\uff0c\u8fd9\u79cd\u5927\u4e00\u7edf\u7684\u5c40\u9762\u5c06\u4e0d\u590d\u5b58\u5728\uff1a
\npublic class Test5{
\n        public static void main(String args[]){
\n                Object r = ()->System.out.println(“hello,lambda”);
\n        }<\/p>\n
}
\n\u7f16\u8bd1\u62a5\u9519\uff1a
\nTest5.java:3: error: incompatible types: Object is not a functional interface
\n                Object r = ()->System.out.println(“hello,lambda”);
\n                           ^
\n1 error
\n\u5f88\u663e\u7136\uff0c\u7f16\u8bd1\u5668\u4f1a\u68c0\u67e5\u53d8\u91cf\u7684\u5f15\u7528\u7c7b\u578b\u91cc\u9762\u662f\u5426\u771f\u7684\u662f\u4e00\u4e2a\u51fd\u6570\u5f0f\u63a5\u53e3\u3002\u90a3\u4e48\u5982\u4f55\u8ba9\u8fd9\u6bb5\u4ee3\u7801\u901a\u8fc7\u7f16\u8bd1\u5462\uff1f
\n\u53ea\u9700\u8981\u52a0\u4e00\u4e2a\u5f3a\u5236\u7c7b\u578b\u8f6c\u6362\u5c31\u53ef\u4ee5\u4e86\uff1a<\/p>\n


public class Test6{\n        public static void main(String args[]){\n                Object r = (Runnable)()->System.out.println(\"hello,lambda\");\n        }\n\n}\n<\/code><\/pre>\n
lambda\u7684\u8bcd\u6cd5\u4f5c\u7528\u57df
\n\u6211\u4eec\u77e5\u9053\uff0c\u5728\u533f\u540d\u5185\u90e8\u7c7b\u4e2d\uff1a<\/p>\n

class Hello {\n  public Runnable r = new Runnable() {\n      public void run() {\n        System.out.println(this);\n        System.out.println(toString());\n      }\n    };\n\n  public String toString() {\n    return \"Hello's custom toString()\";\n  }\n}\n\npublic class InnerClassExamples {\n  public static void main(String... args) {\n    Hello h = new Hello();\n    h.r.run();\n  }\n}\nSystem.out.println(this);\u8fd9\u91cc\u7684this\u6307\u7684\u662f\u533f\u540d\u7c7b\uff0c\u800c\u975eHello\u7c7b\u3002 \n\u60f3\u8981\u5f15\u7528Hello\u7c7b\u9700\u8981Hello.this\u8fd9\u6837\uff1a\nclass Hello {\n  public Runnable r = new Runnable() {\n      public void run() {\n        System.out.println(Hello.this);\n        System.out.println(Hello.this.toString());\n      }\n    };\n}\n<\/code><\/pre>\n
\u8fd9\u79cd\u505a\u6cd5\u975e\u5e38\u7684\u53cd\u4eba\u7c7b\u53cd\u76f4\u89c9\uff01\u770b\u4e0a\u53bb\u5f88\u6076\u5fc3\uff01
\n\u4e0b\u9762\u6211\u4eec\u5c31\u6765\u770b\u4e00\u4e0b\u4f1f\u5927\u7684lambda\u662f\u4ec0\u4e48\u6837\u5b50\u7684\uff1a<\/p>\n
class Hello{\n  public Runnable r = () -> {\n       System.out.println(this);\n       System.out.println(toString());\n  };\n\n  public String toString() {\n      return \"Hello's custom toString()\";\n  }\n}\npublic class Test7{\n  public static void main(String args[]){\n        Hello h = new Hello();\n        h.r.run();\n  }\n}\n<\/code><\/pre>\n
\u8f93\u51fa\uff1a
\nHello’s custom toString()
\nHello’s custom toString()
\nSystem.out.println(this);\u8fd9\u91cc\u7684this\u6307\u7684\u662fHello\uff0c\u800c\u975elambda\u8868\u8fbe\u5f0f\uff01
\n\u4f46\u662f\uff0c\u5982\u679c\u6211\u4eec\u60f3\u5728lambda\u8868\u8fbe\u5f0f\u4e2d\u8fd4\u56delambda\u672c\u8eab\u8be5\u600e\u4e48\u505a\u5462\uff1f
\n\u53d8\u91cf\u6355\u83b7
\n\u533f\u540d\u5185\u90e8\u7c7b\u53ea\u80fd\u5f15\u7528\u4f5c\u7528\u57df\u5916\u9762\u7684final\u7684\u53d8\u91cf\uff0c\u5728lambda\u4e2d\u5bf9\u8fd9\u4e2a\u9650\u5236\u505a\u4e86\u524a\u5f31\uff0c\u53ea\u9700\u8981\u662f\u201c\u7b49\u4ef7final\u201d\u5c31\u53ef\u4ee5\uff0c\u6ca1\u5fc5\u8981\u7528final\u5173\u952e\u5b57\u6765\u6807\u8bc6\u3002<\/p>\n

public class Test8{\n        public static void main(String args[]){\n                String message = \"Howdy, world!\";\/\/\u4e0d\u9700\u8981\u662ffinal\u7684\n                Runnable r = () -> System.out.println(message);\/\/\u8fd9\u91cc\u4e5f\u80fd\u8bbf\u95ee\n                r.run();\n        }\n}\n<\/code><\/pre>\n
\u201c\u7b49\u6548final\u201d\u7684\u610f\u601d\u662f\uff1a\u4e8b\u5b9e\u4e0a\u7684final\uff0c\u6240\u4ee5\uff0c\u4e00\u65e6\u8d4b\u503c\u4e5f\u662f\u4e0d\u53ef\u4ee5\u6539\u53d8\u7684\uff01\u6bd4\u5982\uff1a<\/p>\n
public class Test9{\n  public static void main(String args[]){\n    String message = \"Howdy, world!\";\n    Runnable r = () -> System.out.println(message);\n    r.run();\n    message = \"change it\";\n  }\n}\n<\/code><\/pre>\n
Test9.java:4: error: local variables referenced from a lambda expression must be final or effectively final<\/h5>\n
            Runnable r = () -> System.out.println(message); \n                                                  ^ \n<\/code><\/pre>\n
1 error
\n\u5982\u679c\u4e0a\u9762\u7684\u5185\u5bb9\u770b\u4e0a\u53bb\u5e73\u6de1\u65e0\u5947\u7684\u8bdd\uff0c\u771f\u6b63\u7684\u5927\u6740\u5668\u51fa\u73b0\u4e86\uff1a\u65b9\u6cd5\u5f15\u7528
\n\u6211\u4eec\u6709\u4e00\u4e2a\u8fd9\u6837\u7684\u7c7b\uff1a<\/p>\n
class Person {\n  public String firstName;\n  public String lastName;\n  public int age;\n}\n<\/code><\/pre>\n
\u73b0\u5728\u6211\u4eec\u8981\u628a\u591a\u4e2aPerson\u5bf9\u8c61\u8fdb\u884c\u6392\u5e8f\uff0c\u6709\u65f6\u5019\u662f\u6309\u7167firstName\u6765\u6392\uff0c\u6709\u65f6\u5019\u662f\u6309\u7167lastName\u6216\u8005\u662fage\u6765\u6392\uff0c\u4f7f\u7528lambda\u53ef\u4ee5\u8fd9\u6837\u6765\u505a\uff1a<\/p>\n
class Person{\n  public String firstName;\n  public String lastName;\n  public int age;\n  public Person(String firstName, String lastName, int age){\n    this.firstName = firstName;\n    this.lastName = lastName;\n    this.age = age;\n  }\n  public String toString(){\n    return firstName+\",\"+lastName+\",\"+age;\n  }\n}\npublic class Test10{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 41),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Neward\", 19),\n      new Person(\"Matthew\", \"Neward\", 13)\n    };\n    \/\/sort by firstName\n    Arrays.sort(people, (lhs,rhs)->lhs.firstName.compareTo(rhs.firstName));\n    for(Person p : people){\n      System.out.println(p);\n    }\n  }\n}\n<\/code><\/pre>\n
\u6211\u4eec\u53ef\u4ee5\u628aComparator\u62bd\u53d6\u51fa\u6765\uff0c\u53d8\u6210\u662fPerson\u5bf9\u8c61\u7684\u6210\u5458\u53d8\u91cf\uff1a<\/p>\n
class Person{\n  public String firstName;\n  public String lastName;\n  public int age;\n  public Person(String firstName, String lastName, int age){\n    this.firstName = firstName;\n    this.lastName = lastName;\n    this.age = age;\n  }\n  public String toString(){\n    return firstName+\",\"+lastName+\",\"+age;\n  }\n  public final static Comparator<person> compareFirstName =\n      (lhs, rhs) -> lhs.firstName.compareTo(rhs.firstName);\n\n  public final static Comparator<\/person><person> compareLastName =\n      (lhs, rhs) -> lhs.lastName.compareTo(rhs.lastName);\n\n  public final static Comparator<\/person><person> compareAge =\n      (lhs, rhs) -> lhs.age - rhs.age;\n}\npublic class Test11{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 41),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Neward\", 19),\n      new Person(\"Matthew\", \"Neward\", 13)\n    };\n    Arrays.sort(people, Person.compareFirstName);\/\/\u8fd9\u91cc\u76f4\u63a5\u5f15\u7528lambda\n    for(Person p : people){\n      System.out.println(p);\n    }\n  }\n}\n<\/code><\/pre>\n
\u80fd\u8d77\u5230\u540c\u6837\u7684\u4f5c\u7528\uff0c\u4f46\u662f\u8bed\u6cd5\u770b\u4e0a\u53bb\u5f88\u5947\u602a\uff0c\u56e0\u4e3a\u4e4b\u524d\u6211\u4eec\u90fd\u662f\u521b\u5efa\u4e00\u4e2a\u6ee1\u8db3Comparator\u7b7e\u540d\u7684\u65b9\u6cd5\uff0c\u7136\u540e\u76f4\u63a5\u8c03\u7528\uff0c\u800c\u975e\u5b9a\u4e49\u4e00\u4e2a\u53d8\u91cf\uff0c
\n\u7136\u540e\u5f15\u7528\u8fd9\u4e2a\u53d8\u91cf\uff01\u6240\u4ee5\uff0c\u8fd8\u6709\u8fd9\u4e48\u4e00\u79cd\u8c03\u7528\u65b9\u6cd5\uff1a<\/p>\n
class Person{\n  public String firstName;\n  public String lastName;\n  public int age;\n  public Person(String firstName, String lastName, int age){\n    this.firstName = firstName;\n    this.lastName = lastName;\n    this.age = age;\n  }\n  public String toString(){\n    return firstName+\",\"+lastName+\",\"+age;\n  }\n  public static int compareFirstName(Person lhs, Person rhs){\n    return lhs.firstName.compareTo(rhs.firstName);\n  } \n  public static int compareLastName(Person lhs, Person rhs){\n       return lhs.lastName.compareTo(rhs.lastName);\n  }\n}\npublic class Test12{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 41),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Neward\", 19),\n      new Person(\"Matthew\", \"Neward\", 13)\n    };\n    Arrays.sort(people, Person::compareFirstName);\n    for(Person p : people){\n      System.out.println(p);\n    }\n  }\n}\n<\/code><\/pre>\n
\u770bPerson::compareFirstName\u8fd9\u79cd\u8c03\u7528\u65b9\u5f0f\uff0c
\n\u5982\u679c\u662fstatic\u65b9\u6cd5\u4f7f\u7528\uff1a\u7c7b\u540d::\u65b9\u6cd5\u540d
\n\u5982\u679c\u662finstance\u65b9\u6cd5\uff1ainstance::\u65b9\u6cd5\u540d
\n\u4f46\u662f\uff0c\u4e0a\u9762\u7684\u4ee3\u7801\u8fd8\u662f\u4e0d\u662f\u5f88\u7f8e\u89c2\uff0c\u56e0\u4e3aPerson\u53ea\u662f\u4e00\u4e2a\u6570\u636e\u5bf9\u8c61\uff0c\u5b83\u4e0d\u5e94\u8be5\u7684\u5bf9\u5916\u63d0\u4f9bcompareFirstName\u6216\u8005\u662fcompareLastName\u8fd9\u6837\u7684\u65b9\u6cd5\uff0c
\n\u6211\u4eec\u9700\u8981\u7684\u4ec5\u4ec5\u662f\u6839\u636e\u67d0\u4e2a\u5b57\u6bb5\u6392\u5e8f\u800c\u5df2\uff01\u5f88\u5e78\u8fd0\u7684\u662fjdk\u7684api\u5e2e\u6211\u4eec\u505a\u4e86\u8fd9\u4ef6\u4e8b\uff1a<\/p>\n
import java.util.*;\nclass Person{\n  public String firstName;\n  public String lastName;\n  public int age;\n  public Person(String firstName, String lastName, int age){\n    this.firstName = firstName;\n    this.lastName = lastName;\n    this.age = age;\n  }\n  public String getFirstName(){\n    return this.firstName;\n  }\n  public String getLastName(){\n    return this.lastName;\n  }\n  public String toString(){\n    return firstName+\",\"+lastName+\",\"+age;\n  }\n}\npublic class Test13{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 41),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Neward\", 19),\n      new Person(\"Matthew\", \"Neward\", 13)\n    };\n    Arrays.sort(people, Comparator.comparing(Person::getFirstName));\n    for(Person p : people){\n      System.out.println(p);\n    }\n  }\n}\nArrays.sort(people, Comparator.comparing(Person::getFirstName));\n<\/code><\/pre>\n
\u8fd9\u91cc\u8c03\u7528\u4e86Comparator.comparing\u65b9\u6cd5\uff0c
\n\u4f46\u662f\u6ce8\u610f\u8fd9\u91cc\u7684Person::getFirstName\uff0c\u5f88\u663e\u7136getFirstName()\u5e76\u4e0d\u662fstatic\u7684\uff0c\u8fd9\u662fjdk\u505a\u4e86\u5c01\u88c5\u7684\u7f18\u6545\uff01
\n\u8fd9\u6837\u505a\u5c31\u975e\u5e38\u5b8c\u7f8e\u4e86\uff01
\n\u5047\u5982\u6211\u4eec\u7684\u6392\u5e8f\u7b97\u6cd5\u6539\u4e3a\uff1a\u5148\u6309\u7167lastName\uff0c\u7136\u540e\u6309\u7167age\u6392\u5e8f\u5462\uff1f<\/p>\n
public class Test15{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 10),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Naward\", 19),\n      new Person(\"Matthew\", \"Nmward\", 13)\n    };\n    Collections.sort(Arrays.asList(people), (lhs, rhs)->{\n      if(lhs.getLastName().equals(rhs.getLastName())){\n        return lhs.getAge()-rhs.getAge();\n      }else{\n        return lhs.getLastName().compareTo(rhs.getLastName());\n      }\n    });\n    for(Person p : people){\n      System.out.println(p);\n    }\n  }\n}\n<\/code><\/pre>\n
\u5f88\u663e\u7136\uff0c\u5e94\u8be5\u8fd8\u6709\u66f4\u597d\u7684\u5b9e\u73b0\u65b9\u5f0f\uff1a<\/p>\n
public class Test16{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 10),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Naward\", 19),\n      new Person(\"Matthew\", \"Nmward\", 13)\n    };\n    Collections.sort(Arrays.asList(people),Comparator.comparing(Person::getLastName).thenComparing(Person::getAge));\n    for(Person p : people){\n      System.out.println(p);\n    }\n  }\n}\nComparator.comparing(Person::getLastName).thenComparing(Person::getAge)\uff1a\u7b80\u76f4\u5e05\u5446\u4e86\uff01 \n<\/code><\/pre>\n
\u8fd8\u6709\u66f4\u591a\u7684\u8bf8\u5982\uff1aandThen()\u8fd9\u6837\u7684\u65b9\u6cd5\uff0c\u53ef\u4ee5\u67e5api\u3002
\n\u865a\u65b9\u6cd5\u6269\u5c55
\n\u56e0\u4e3a\u63a5\u53e3\u53ef\u4ee5\u6709default\u65b9\u6cd5\uff0c\u6240\u4ee5\u5f88\u591a\u7c7b\u5e93\u90fd\u91cd\u5199\u4e86\uff0c\u52a0\u5165\u4e86\u4e00\u4e9bdefault\u7684\u65b9\u6cd5\uff0c\u6bd4\u5982\uff1a<\/p>\n
interface Iterator<t> { \n  boolean hasNext(); \n  T next(); \n  void remove(); \n  void skip(int i) default { \n    for (; i > 0 && hasNext(); i--) next(); \n  } \n}  \n<\/code><\/pre>\n
skip(i)\u5c31\u662f\u4e00\u4e2adefault\u65b9\u6cd5\uff0c\u8fd9\u6837\u6240\u6709\u7684Iterator\u7684\u5b50\u7c7b\u90fd\u5177\u6709\u4e86\u4e00\u4e2a\u53ebskip\u7684\u65b9\u6cd5\uff01
\n\u4f46\u662f\uff0c\u5927\u5bb6\u5bf9default\u65b9\u6cd5\u7684\u4e89\u8bae\u8fd8\u662f\u6bd4\u8f83\u5927\u7684\uff0c\u6bd4\u5982\uff1a<\/p>\n
interface I1 {\n  public default void print(){\n    System.out.println(\"I1\");\n  }\n  public void hello();\n}\ninterface I2{\n  public default void print(){\n    System.out.println(\"I2\");\n  }\n  public void world();\n}\nclass Impl implements I1,I2{\n  public void hello(){\n  }\n  public void world(){\n  }\n}\n<\/code><\/pre>\n
\u5982\u679c\u5728Impl\u4e0a\u8c03\u7528print\u4f1a\u600e\u6837\u5462\uff1f\u8fd9\u4e0d\u5c31\u662f\u4f20\u8bf4\u4e2d\u7684\u591a\u7ee7\u627f\u4e48\uff1f\u60f3\u77e5\u9053\u7ed3\u679c\u7684\u8bdd\uff0c\u81ea\u5df1\u8bd5\u4e00\u4e0b\u5c31\u53ef\u4ee5\u4e86\uff0c\u54c8\u54c8
\nStream\uff1a
\n\u4e4b\u524d\u7684\u6587\u7ae0\u5df2\u7ecf\u6709\u4ecb\u7ecd\uff0c\u4e0b\u9762\u53ea\u636e\u4e00\u4e9b\u4f7f\u7528\u7684\u4f8b\u5b50\uff1a
\n\u8fc7\u6ee4age>12\u7684\u5143\u7d20\uff1a<\/p>\n
people\n      .stream()\n      .filter(it -> it.getAge() >= 21) ;\n\u8fc7\u6ee4age>12\u7684\u5143\u7d20,\u5e76\u8f93\u51fa\uff1a\npeople.stream()\n      .filter((it) -> it.getAge() >= 21)\n      .forEach((it) -> \n        System.out.println(\"Have a beer, \" + it.getFirstName()));\njdk\u9884\u5b9a\u4e49\u7684Predicate\uff1a\nPredicate<person> drinkingAge = (it) -> it.getAge() >= 21;\nPredicate<\/person><person> brown = (it) -> it.getLastName().equals(\"Brown\");\npeople.stream()\n      .filter(drinkingAge.and(brown))\n      .forEach((it) ->System.out.println(\"Have a beer, \" + it.getFirstName()));\nmap\uff1a\nIntStream ages =\n  people.stream()\n    .mapToInt((it) -> it.getAge()); \n\/\/sum\uff1a\nint sum = people.stream()\n        .mapToInt(Person::getAge)\n        .sum();\n<\/code><\/pre>\n
\u91cd\u70b9\u8bf4\u4e0breduce\uff1a<\/p>\n
public class Test17{\n        public static void main(String args[]){\n                List<integer> values = Arrays.asList(1,2,3,4,5);\n                int sum = values.stream().reduce(0, (l,r)->l+r);\n                System.out.println(sum);\n        }\n}\n<\/code><\/pre>\n
reduce(0, (l,r)->l+r)\u7684\u5de5\u4f5c\u539f\u7406\u662f\uff1a\u7b2c\u4e00\u4e2a\u53c2\u65700\u4f5c\u4e3a\u540e\u9762lambda\u8868\u8fbe\u5f0f\u7684\u5de6\u64cd\u4f5c\u6570\uff0c\u7136\u540e\u4ecestream\u4e2d\u53d6\u51fa\u4e00\u4e2a\u5143\u7d20\u4f5c\u4e3a\u53f3\u64cd\u4f5c\u6570\uff0c
\n\u4e8c\u8005\u8fd0\u7b97\u7684\u7ed3\u679c\u4f5c\u4e3a\u4e0b\u4e00\u6b21\u8fd0\u7b97\u7684\u5de6\u64cd\u4f5c\u6570\uff0c\u4f9d\u6b21\u5faa\u73af\u3002
\n\u6700\u540e\u770b\u4e00\u4e2a\u597d\u73a9\u7684\u4f8b\u5b50\uff1a<\/p>\n
class Person{\n  public String firstName;\n  public String lastName;\n  public int age;\n  public Person(String firstName, String lastName, int age){\n    this.firstName = firstName;\n    this.lastName = lastName;\n    this.age = age;\n  }\n  public String getFirstName(){\n    return this.firstName;\n  }\n  public String getLastName(){\n    return this.lastName;\n  }\n  public int getAge(){\n    return this.age;\n  }\n  public String toString(){\n    return firstName+\",\"+lastName+\",\"+age;\n  }\n  public String toJson(){\n    return \"{\"+\n        \"firstName:\\\"\"+firstName+\"\\\",\"+\n        \"lastName:\\\"\"+lastName+\"\\\",\"+\n        \"age:\"+age +\n        \"}\";\n  }\n}\npublic class Test18{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 10),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Naward\", 19),\n      new Person(\"Matthew\", \"Nmward\", 13)\n    };\n    String json = Arrays.asList(people).stream().map(Person::toJson).reduce(\"[\",(l,r)->l + (l.equals(\"[\")?\"\":\",\") + r)+\"]\";\n    System.out.println(json);\n  }\n}\n\u8f93\u51fa\u7ed3\u679c\uff1a \n[{firstName:\"Ted\",lastName:\"Neward\",age:10},{firstName:\"Charlotte\",lastName:\"Neward\",age:41},{firstName:\"Michael\",lastName:\"Naward\",age:19},{firstName:\"Matthew\",lastName:\"Nmward\",age:13}] \n<\/code><\/pre>\n
\u8fd8\u53ef\u4ee5\u8fd9\u6837\uff1a<\/p>\n
public class Test19{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 10),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Naward\", 19),\n      new Person(\"Matthew\", \"Nmward\", 13)\n    };\n    String joined = Arrays.asList(people).stream().map(Person::toJson).collect(Collectors.joining(\", \"));\n        System.out.println(\"[\" + joined + \"]\"); \n  }\n}\n<\/code><\/pre>\n
\u66f4\u8fdb\u4e00\u6b65\uff1a<\/p>\n
public class Test20{\n  public static void main(String args[]){\n    Person people[] = new Person[]{\n      new Person(\"Ted\", \"Neward\", 10),\n      new Person(\"Charlotte\", \"Neward\", 41),\n      new Person(\"Michael\", \"Naward\", 19),\n      new Person(\"Matthew\", \"Nmward\", 13)\n    };\n    String json = Arrays.asList(people).stream().map(Person::toJson).collect(Collectors.joining(\", \", \"[\", \"]\"));\n    System.out.println(json);\n  }\n}\n<\/code><\/pre>\n
\u5982\u679c\u53ea\u80fd\u7528\u4e00\u4e2a\u5b57\u6765\u5f62\u5bb9\uff0c\u90a3\u5c31\u662fperfect\uff01
\n<\/integer><\/person><\/t><\/person><\/string><\/p>\n","protected":false},"excerpt":{"rendered":"
\u53c2\u8003\uff1a http:\/\/www.oracle.com\/technetwork\/articles\/java\/arc […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"aside","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[3],"tags":[],"class_list":["post-69","post","type-post","status-publish","format-aside","hentry","category-tech","post_format-post-format-aside"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.espandy.com\/index.php?rest_route=\/wp\/v2\/posts\/69","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.espandy.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.espandy.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.espandy.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.espandy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=69"}],"version-history":[{"count":3,"href":"https:\/\/www.espandy.com\/index.php?rest_route=\/wp\/v2\/posts\/69\/revisions"}],"predecessor-version":[{"id":72,"href":"https:\/\/www.espandy.com\/index.php?rest_route=\/wp\/v2\/posts\/69\/revisions\/72"}],"wp:attachment":[{"href":"https:\/\/www.espandy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=69"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.espandy.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=69"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.espandy.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=69"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}