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java – What are the functions of an array of an arrayList?-Exceptionshub

Posted by: admin February 25, 2020 Leave a comment


I tried to do:

static boolean newTrait(ArrayList<Integer> population, int[] traits) {
        for(int i = 0; i < 25; i++) {
            for(int j = 0; j < 625; j++) {
                if(traits[j].equals(population[i].get(i))) {
                    return false;
        return true;

The java compiler said that I had an “unresolved compiler issue.”

Can anyone help?

How to&Answers:

[X] operator is for arrays. You don’t have an ArrayList array you just have an ArrayList<> which, although it has “Array” in the name, is not an array and so cannot be accessed with [X]. ArrayList is an object with regular methods.

It’s perfectly valid to have an ArrayList array

static boolean newTrait(ArrayList<Integer>[] population, int[] traits)

where each element in the population array IS A ArrayList. In which case you would first need to access the element in the array (via [X]) and then access the elements IN the ArrayList using get()

e.g. get the first element of the array

 ArrayList<Integer> firstList = population[0];

then get the Xth item in the list



All simple types (not objects) do not have any methods. In your case neither the array not the int values inside the array have methods.


if(traits[j] == population.get(i)) 
    return false;

This compares an int on the left side with an Integer on the right side. For int the == operator is correct but it would be wrong for Integers. However in this case the compiler does automatically ‘unbox’ the Integer on the right side to int.

Notice that I removed the wrong [i] after population as well. Population is not an array.