flatMap

定义

  1. <R> Stream<R> flatMap(Function<? super T, ? extends Stream<? extends R>> mapper);

功能

将Function转化后的Stream合并成一个Stream。

案例

  1. @Test
  2. public void mergeMapValuesTest(){
  3.     Map<Integer, ListContainer> map = Maps.newHashMap();
  4.     List<AClass> aClassList1 = Lists.newArrayList();
  5.     AClass aClass = new AClass(1, "zhuoli1", "haha1");
  6.     aClassList1.add(aClass);
  7.     aClassList1.add(new AClass(2, "zhuoli2", "haha2"));
  8.     aClassList1.add(new AClass(3, "zhuoli3", "haha3"));
  10.     List<AClass> aClassList2 = Lists.newArrayList();
  11.     aClassList2.add(aClass);
  12.     aClassList2.add(new AClass(5, "zhuoli5", "haha5"));
  13.     aClassList2.add(new AClass(6, "zhuoli6", "haha6"));
  15.     /*交集*/
  16.     /*[AClass(id=1, name=zhuoli1, description=haha1)]*/
  17.     List<AClass> intersectResult = aClassList1.stream().filter(aClassList2::contains).collect(Collectors.toList());
  18.     System.out.println(intersectResult);
  20.     /*并集*/
  21.     List<AClass> unionResult = Stream.of(aClassList1, aClassList2).flatMap(Collection::stream).distinct().collect(Collectors.toList());
  22.     assertEquals(unionResult.size(), 5);
  23.     System.out.println(unionResult);
  25.     /*差集*/
  26.     /*[AClass(id=2, name=zhuoli2, description=haha2), AClass(id=3, name=zhuoli3, description=haha3)]*/
  27.     List<AClass> differenceResult = aClassList1.stream().filter(x -> !aClassList2.contains(x)).collect(Collectors.toList());
  28.     System.out.println(differenceResult);
  30.     map.put(1, new ListContainer(aClassList1));
  31.     map.put(2, new ListContainer(aClassList2));
  33.     /*合并多个list*/
  34.     List<AClass> aClassListResult = map.values().stream().flatMap(listContainer -> listContainer.getLst().stream()).collect(Collectors.toList());
  35.     /*注意跟并集的区别*/
  36.     assertEquals(aClassListResult.size(), 6);
  37.     System.out.println(aClassListResult);
  38. }