How to find the maximum value from a ArrayList which has both int and double values?

Question

I tried this what am i doing wrong or what should i do.I am a beginner CS student trying to solve this question. The error i get is in image format here: Error i get when i try to runprogram

import java.util.*;
public class maximum
{
       public static void main(String[]args)
       {
       //Creates new array list
       ArrayList list = new ArrayList();
       
       //Adds the numbers in the ArrayList
       Collections.addAll(list,5,2,-8,9,5.5,7,0);
       
       //Stores the highest number in new arraylist
       ArrayList highestNumber = new ArrayList();
       highestNumber.add(Collections.max(list));
       
       // Prints highestNumber
       System.out.println(highestNumber);
       }
}

Answer 1

First step: Change the List type to Number, which is the superclass of all java's boxed numeric primitives.

Then, find the max by comparing Number#doubleValue():

ArrayList<Number> list = new ArrayList<>();
Collections.addAll(list, 5, 2, -8, 9, 5.5, 7, 0);
ArrayList<Number> highestNumber = new ArrayList<>();
highestNumber.add(Collections.max(list, Comparator.comparing(Number::doubleValue)));

Since all int may be safely converted to a Double, this code is completely safe to use with a mix of doubles and ints.