如何在java中过滤List<String>中的ArrayList<List<String>

Question

如何筛选出ArrayList中列表中索引0中的字符串"1“，如下所示

List<List<String>> a = new ArrayList<List<String>>();
a.add(Arrays.asList("1","2","3"));
a.add(Arrays.asList("4","5","6"));
a.add(Arrays.asList("2","1","8"));
a.add(Arrays.asList("1","1","8"));

do过滤器后的预期结果是:在ArrayList中列出索引0、3

Answer 1

检索索引：

int[] indexArray = IntStream.range(0, a.size()).filter(x -> a.get(x).get(0).equals("1")).toArray();

要检索实际列表，请执行以下操作：

List<List<String>> resultSet = a.stream().filter(x -> x.get(0).equals("1")).collect(Collectors.toList());