使用Java 8 lambda或stream api过滤列表

Question

My class structure -

class A {
    List<B> bList;
}

class B {
   List<C> cList;
}

Now i have a list of class A and i want to filter it based on condition that c.size() > 0. I can filter it using 2 for loop one for list A and other for list B but i want to know can i filter list of A using java stream api without for loop.

My current code (updated code) -

List<A> result = = new ArrayList<>();
for (A a : aList) {
   List<B> tempBList = = new ArrayList<>();
   for (B b : a.getBList) {
       if (b.getCList.size() > 0) {
          tempBList.add(b);
       }
   }

   if (tempBList.size() > 0) {
       a.setBList(tempBList);
       result.add(a);
   }
}

Answer 1

Yes, you can:

List<A> result =
    listOfA.stream()
           .filter(a -> a.b.stream().anyMatch(b -> b.c.size() > 0))
           .collect(Collectors.toList());

This is assuming you want to add each instance of A that passes that filter to the output List once.

Answer 2

Try this. items is the list which you want to filter.

    List<A> result = new ArrayList<>();

    result = items.stream().filter(a -> a.b.stream().filter(b -> b.c.size() > 0).count() > 0).collect(Collectors.toList());