Collector.groupingby () ?? ???, ?? ??? ???? ?? ?? ??; 2. Collectors.partitioningby () ?? ??? ?? ???; 3. Collector.joining () ?? ??? ???, ?? ?? ?, ??? ? ???; 4. SummarizingInt ()? ?? ?? ???? ??? ?????. 5. ??? ??? ?????? ?? ? ?? ???; 6. Collectingandthen ()? ??? ?? ??? ?????. ? ?? ???? ??? ???? ??? ??? ??? ?? ??? ?? ???? ???? ??? ????? ????? ????? ?? ? ????.

Java? Stream API? ?? ???? ?????? ??? ???? Collectors ??? ??? ??? ??? ???? ?????. Collectors.toList() ? Collectors.toMap() ? ?? ????? ???? ?? Collectors ???? ???? ??? ??? ?? ?? ?? ??? ?? ??? ?????. ??? ????? ?? ?? ???? ????? ????? ???? ???? ?? ?????.

1. groupingBy() ? ??? ??? ???

?? ??? ??? ? ??? Collectors.groupingBy() ???. ??? ?? ??? ???? ??? ???? ?????.

 list <string> words = arrays.aslist ( "Apple", "Banana", "Cherry", "Date");

map <integer, list <string >> groupedBylength = words.stream ()
    .Collect (Collectors.groupingby (String :: length));

// ?? : {4 = [??], 5 = [Apple], 6 = [???, ??]}

?? ?? ??? ???? ???? ? ??? ??? ?? ? ? ????.

 ?? <integer, long> countbylength = words.stream ()
    .collect (collectors.groupingby (??? :: ??, collectors.counting ()));

// ?? : {4 = 1, 5 = 1, 6 = 2}

?? ???? ?? ??, ?? ?? ??? ?? ???? ???? ? ?? ?????.

2. partitioningBy()

?? ??? ?? ???? ? ???? ?? ???? ?? partitioningBy() ??????.

 Map <boolean, list <integer >> evenodd = arrays.aslist (1, 2, 3, 4, 5) .stream ()
    .collect (Collectors.PartitioningBy (n-> n % 2 == 0));

// ?? : {false = [1, 3, 5], true = [2, 4]}

groupingBy() ? ????? ?? ??? ???? ?????.

 ?? <??, ??> sumpartition = arrays.aslist (1, 2, 3, 4, 5) .stream ()
    .Collect (Collectors.PartitioningBy (
        n -> n % 2 == 0,
        Collectors.summmingint (Integer :: Intvalue)
    ));

// ?? : {false = 9, true = 6}

??? Pass/Fail, Active/Neactive ?? ?? ?? ??? ??????.

3. joining() ? ?? ??? ??

????? ???? ???????? Collectors.joining() ? ???? ??????.

 list <string> names = arrays.aslist ( "Alice", "Bob", "Charlie");

joined = names.stream ()
    .collect (collectors.joining ( ",", "names :", "));

// ?? : "?? : Alice, Bob, Charlie."

????? :

• ?? ?? ( ", " )
• ??? ??? ( "Names: " )
• ??? ??? ( "." )

?? ?? ?? ?? CSV? ?? ???? ???? ? ?????.

4. ?? ??? ??

Java? ?? ????? ?? ???? ?????.

• Collectors.summingInt() , summingLong() , summingDouble()
• Collectors.averagingInt() ?
• Collectors.maxBy() , minBy() Comparator

?:

 ?? <integer> ?? = arrays.aslist (1, 2, 3, 4, 5);

intsummarystatistics ?? = ?? .Stream ()
    .Collect (Collectors.summarizingInt (Integer :: intvalue));

// stats.getSum () → 15
// stats.getAverage () → 3.0
// stats.getMax () → 5

summarizingInt() ? ?? ??? ?? ?? ?? ?? ?????.

5. ??? ???? ?????

groupingBy() , partitioningBy() ?? mapping() ? ??? ?? ???? ?? ? ? ????.

?? ??, City? ?? ???? ??? ?? ? ????.

 map <string, list <string >> namesbycity = people.stream ()
    .collect (Collectors.groupingby (
        ?? :: getcity,
        Collectors.mapping (person :: getname, collector.tolist ())
    ));

?? ?? ? ?? ??? ?????.

 Map <String, Double> avgageByDept = Employec.Stream ()
    .collect (Collectors.groupingby (
        ?? :: GetDepartment,
        Collectors.avagingInt (?? :: getage)
    ));

? ?? ???? Collectors ?? ???? ????.

6. collectingAndThen()

??? ??? ?? ?? ??? ???? ?? ?, ?? ??? ????? ???? ?? ?????.

 ??? maxname = names.stream ()
    .Collect (Collectors.collectingandthen (
        Collectors.maxby (String :: Compareto),
        ?? ?? :: ????
    ));

??? ???? ???? ??? ??? ??? ?????. ?? ??? ????? ?? ? ? ??????.

?????? : ?? ???? ? Optional ???? Optional::get ? ?? ????!

?? ??

toList() ? toMap() ?? ?? ??? ??? ? ? ?? Collectors ?? ??? ?? ?? ??? ????.

• ??? ????? ????
• ?? ?? (????? ?? ??)
• ?? ????? ???? ??? ??? ??????

? ?? ???? ?? ?? ?? ? ??? ??? ??? ???? ???? ????? ?? ?? ??? ??? ???????.

????? groupingBy , partitioningBy ? ?? ? ???? ???? ???? ???? ??? ???? ?????.

? ??? Java Stream Collectors :`Tolist ()`?`tomap ()`? ???? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!