我是Java流的新手，所以希望有人可以对此进行调试。我不明白我怎么得到最低的数字。

public class main {

    public static void main(String[] args) {
        Product p1 = new Product("1","name1",1000);
        Product p2 = new Product("2","name2",2000);
        Product p3 = new Product("3","name3",3000);
        Product p4 = new Product("4","name4",4000);

        HashMap<String,Product> map = new  HashMap<String,Product>();

        map.put(p1.getId(),p1);
        map.put(p2.getId(),p2);
        map.put(p3.getId(),p3);
        map.put(p4.getId(),p4);


        int i = (Integer) map.values().stream()
                .map(x -> (Integer) Integer.valueOf(x.getId()))
                .max(Integer::max).get();

        System.out.println(i);
    }

}