max nr finder

import java.io.InputStream;
import java.util.Collections;
import java.util.Scanner;
import java.util.Vector;

class NegNrEx extends Exception {
    public NegNrEx(int nr) {
        super("The entered nr(" + nr + ") is < 0");
    }
}

class MaxNrFinder {
    private final Vector<Integer> vector;
    private final Scanner scanner;

    public MaxNrFinder(final InputStream inputStream) {
        vector = new Vector<>();
        scanner = new Scanner(inputStream);
    }

    public void read() throws NegNrEx {
        while (true) {
            int nr = scanner.nextInt();
            if (nr < 0) {
                throw new NegNrEx(nr);
            }
            vector.add(nr);
        }
    }

    public int findMax() {
        if (vector.isEmpty()) {
            return -1;
        }
        return Collections.max(vector);
    }
}

public class Main {
    public static void main(String[] args) {
        var mnf = new MaxNrFinder(System.in);
        try {
            mnf.read();
        } catch (NegNrEx e) {
            System.err.println(e.getMessage());
        } finally {
            System.out.println("max: " + mnf.findMax());
        }
    }
}