Java, Lambda: How to pick a List from a Class with several Lists of different Types? [duplicate]

I believe passing a getter Function that returns the required List can work:

static <T> List<T> getAllOccurrencesForType(Function<Records,List<T>> getter, List<Records> allRecords) {
    return allRecords.stream()
                     .flatMap(r->getter.apply(r).stream())
                     .collect(Collectors.toList());
}

And then you call it with:

List<Type1> getAllOccurrencesForType (Records::getListOfType1,allRecords);

Here's a full example:

class Records {
    List<String> listOfType1;
    List<Integer> listOfType2;
    List<Double> listOfType3;
    public Records (List<String> l1, List<Integer> l2, List<Double> l3) {
      listOfType1 = l1;
      listOfType2 = l2;
      listOfType3 = l3;
    }
    public List<String> getListOfType1() {
      return listOfType1;
    }
    public List<Integer> getListOfType2(){
      return listOfType2;
    }
    public List<Double> getListOfType3(){
      return listOfType3;
    }
}

Some main method:

 List<Records> recs = new ArrayList<> ();
 recs.add (new Records (Arrays.asList ("a","b"), Arrays.asList (1,2), Arrays.asList (1.1,4.4)));
 recs.add (new Records (Arrays.asList ("c","d"), Arrays.asList (4,3), Arrays.asList (-3.3,135.3)));
 List<String> allStrings = getAllOccurrencesForType(Records::getListOfType1,recs);
 List<Integer> allIntegers = getAllOccurrencesForType(Records::getListOfType2,recs);
 List<Double> allDoubles = getAllOccurrencesForType(Records::getListOfType3,recs);
 System.out.println (allStrings);
 System.out.println (allIntegers);
 System.out.println (allDoubles);

output:

[a, b, c, d]
[1, 2, 4, 3]
[1.1, 4.4, -3.3, 135.3]