public class A
{
    String name;
    String getName(){return name;}
}

List<A> list_a = new ArrayList<>();
//add n objects into list_a

final int max_len = list_a.stream().max(Comparator.comparingInt(A::getName::length));

list_a.stream()
      .max(Comparator.comparingInt(A::getName::length));

OptionalInt maxOpt  = list_a.stream()
                            .map(A::getName)
                            .mapToInt(String::length)
                            .max();

int max = maxOpt.orElse(-1); //will return value held by maxOpt, or -1 if there is no value

A a = Collections.max(list, Comparator.comparing(obj -> obj.getName().length()));
int maxLen = a.getName().length();

OptionalInt oi = list_a.stream()
                 .map(A::getName)
                 .mapToInt(String::length)
                 .max()

final int max_len = oi.orElse(0); //defaulting to 0

final int max_len = list_a.stream()
                .max(Comparator.comparingInt(a ->
                     a.getName().length())) //need a lambda
                .map(A::getName)
                .map(String::length)
                .orElse(0); //defaulting to 0