How to get maximum value from the Collection (for example ArrayList)?

This question is almost a year old but I have found that if you make a custom comparator for objects you can use Collections.max for an array list of objects.

import java.util.Comparator;

public class compPopulation implements Comparator<Country> {
    public int compare(Country a, Country b) {
        if (a.getPopulation() > b.getPopulation())
            return -1; // highest value first
        if (a.getPopulation() == b.Population())
            return 0;
        return 1;
    }
}
ArrayList<Country> X = new ArrayList<Country>();
// create some country objects and put in the list
Country ZZ = Collections.max(X, new compPopulation());

public int getMax(ArrayList list){
    int max = Integer.MIN_VALUE;
    for(int i=0; i<list.size(); i++){
        if(list.get(i) > max){
            max = list.get(i);
        }
    }
    return max;
}

From my understanding, this is basically what Collections.max() does, though they use a comparator since lists are generic.

You can use the Collections API to achieve what you want easily - read efficiently - enough Javadoc for Collections.max

Collections.max(arrayList);

Returns the maximum element of the given collection, according to the natural ordering of its elements. All elements in the collection must implement the Comparable interface.