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  1. import java.util.ArrayList;
  2. import java.util.Date;
  3. import java.util.List;
  4. import java.util.Map;
  5. import java.util.stream.Collectors;
  6. import java.util.function.*;
  7. import java.util.stream.*;
  8. import static java.util.stream.Collectors.*;
  9.  
  10. class LambdaTest {
  11.     public static void main(String[] args) {
  12.         List<Emp> list = new ArrayList<>();
  13.  
  14.         Dept dept1 = new Dept(1);
  15.         Dept dept2 = new Dept(2);
  16.         Dept dept3 = new Dept(3);
  17.  
  18.         list.add(new Emp(dept1, 500));
  19.         list.add(new Emp(dept1, 1000));
  20.         list.add(new Emp(dept1, 1500));
  21.         list.add(new Emp(dept1, 2000));
  22.  
  23.         list.add(new Emp(dept2, 1500));
  24.         list.add(new Emp(dept2, 2000));
  25.         list.add(new Emp(dept2, 2500));
  26.         list.add(new Emp(dept2, 3000));
  27.  
  28.         list.add(new Emp(dept3, 0));
  29.         list.add(new Emp(dept3, 100));
  30.         list.add(new Emp(dept3, 200));
  31.         list.add(new Emp(dept3, 500));
  32.  
  33.         new LambdaTest().rankedBySalAndFilter(list);
  34.     }
  35.  
  36.  
  37.     public static <T, A, R> Collector<T, ?, R> filtering(Predicate<? super T> predicate, Collector<? super T, A, R> collector) {
  38.         BiConsumer<A, ? super T> downstream = collector.accumulator();
  39.         return Collector.<T, A, R>of(collector.supplier(),
  40.                 (a, t) -> {if (predicate.test(t)) downstream.accept(a, t);},
  41.                 collector.combiner(), collector.finisher(),
  42.                 collector.characteristics().stream().toArray(Collector.Characteristics[]::new));
  43.     }
  44.  
  45.     void rankedBySalAndFilter(List<Emp> list) {
  46.         Map<Dept, Long> map = list.stream()
  47.             .collect(groupingBy(emp -> emp.dept, filtering(emp -> emp.sal > 1000, counting())));
  48.  
  49.         System.out.println(map);
  50.     }
  51.  
  52.     static class Emp {
  53.         Emp(Dept dept, Integer sal) {
  54.             this.dept = dept;
  55.             this.sal = sal;
  56.         }
  57.  
  58.         Integer empno;
  59.         Dept dept;
  60.         String ename;
  61.         String job;
  62.         Integer mgr;
  63.         Date hiredate;
  64.         Integer sal;
  65.         Integer comm;
  66.     }
  67.  
  68.     static class Dept {
  69.         Dept(Integer deptno) {
  70.             this.deptno = deptno;
  71.         }
  72.  
  73.         Integer deptno;
  74.         String dname;
  75.         String loc;
  76.  
  77.         @Override
  78.         public String toString() {
  79.             return "deptno" + deptno;
  80.         }
  81.     }
  82. }
  83.  
Success #stdin #stdout 0.26s 321152KB
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Standard input is empty
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{deptno3=0, deptno2=4, deptno1=2}
https://ideone.com/83Lzb7
language:
Java (HotSpot 12)
created:
8 years ago
visibility:
secret

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