java求非布尔BiFunction

@FunctionalInterface
public interface BiFunction<T, U, R> {
    R apply(T t, U u);
}

List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
BiFunction<Integer, Integer, Integer> add = (a, b) -> a + b;
numbers.stream()
       .reduce(add)
       .ifPresent(System.out::println); // 输出15

class Person {
    private String name;
    private int age;
    
    // 省略构造函数和getter/setter方法
    
    public static Person merge(Person p1, Person p2) {
        BiFunction<Person, Person, Person> mergeAge = (p, q) -> {
            p.setAge(p.getAge() + q.getAge());
            return p;
        };
        return mergeAge.apply(p1, p2);
    }
}

Person person1 = new Person("Alice", 25);
Person person2 = new Person("Bob", 30);
Person mergedPerson = Person.merge(person1, person2);
System.out.println(mergedPerson.getAge()); // 输出55

BiFunction<Integer, Integer, Integer> gcd = (a, b) -> {
    while (b != 0) {
        int temp = b;
        b = a % b;
        a = temp;
    }
    return a;
};

System.out.println(gcd.apply(12, 18)); // 输出6