Question

(Java Programmin):

Sum() and max() in ArrayList

a. Write a method that returns the maximum value in an ArrayList of integers. The method returns null if the list is null or the list size is 0.         

public static Integer max(ArrayList<Integer> list)

b. Write a method that returns the sum of all numbers in an ArrayList:

public static Integer sum(ArrayList<Integer> list)

c. Write a test program that prompts the user to enter a sequence of numbers ending with 0, and invokes sum and max methods to output the sum and the largest number in the input.

Answer 1

import java.util.ArrayList;
import java.util.Scanner;

public class MaxAndSum {

    public static Integer max(ArrayList<Integer> list) {
        if(list == null || list.isEmpty()) return null;
        Integer num = list.get(0);
        for(int i = 0; i < list.size(); ++i) {
            if(list.get(i).compareTo(num) > 0) {
                num = list.get(i);
            }
        }
        return num;
    }

    public static Integer sum(ArrayList<Integer> list) {
        Integer total = 0;
        for(int i = 0; i < list.size(); ++i) {
            total += list.get(i);
        }
        return total;
    }

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        ArrayList<Integer> list = new ArrayList<>();
        Integer num;
        while (true) {
            System.out.print("Enter a number(0 to exit): ");
            num = in.nextInt();
            if(num == 0) break;
            list.add(num);
        }
        System.out.println("Maximum of entered numbers is " + max(list));
        System.out.println("Sum of entered numbers is " + sum(list));
    }

}

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