Optional

Optional<T> is a box that holds a value or nothing, and forces the caller to think about the nothing case. Optional.of(x), Optional.empty(), and Optional.ofNullable(maybeNull) make one; isPresent(), orElse(fallback), map(f), and ifPresent(action) use it. Returning Optional<Book> from a search says "may not be found" in the signature, where returning null says nothing and crashes later.

Streams return optionals from findFirst() and max(...). The rule of thumb: use Optional as a return type for lookups that can miss; do not store it in fields or pass it as a parameter.

Optional<String> first = words.stream().filter(w -> w.startsWith("b")).findFirst();
System.out.println(first.orElse("none"));
System.out.println(first.map(String::length).orElse(0));

Your task

Write static Optional<String> firstLong(List<String> words, int min) returning the first word longer than min characters, static String firstLongOr(List<String> words, int min, String fallback) using it, and static Optional<Integer> parse(String text) returning the number in the text or an empty optional when it is not a whole number.

import java.util.*;

public class Main {
    static Optional<String> firstLong(List<String> words, int min) {
        return words.stream().filter(w -> w.length() > min).findFirst();
    }

    static String firstLongOr(List<String> words, int min, String fallback) {
        return firstLong(words, min).orElse(fallback);
    }

    static Optional<Integer> parse(String text) {
        try {
            return Optional.of(Integer.parseInt(text));
        } catch (NumberFormatException e) {
            return Optional.empty();
        }
    }

    public static void main(String[] args) {
        System.out.println(firstLongOr(List.of("a", "abcd"), 3, "none") + " " + parse("42").orElse(-1));
    }
}