Java ArrayList for integers

Question

I have values that I\'d like to add into an ArrayList to keep track of what numbers have shown up. The values are integers so I created an ArrayList;

ArrayLi         


        

Answer 1

you should not use Integer[] array inside the list as arraylist itself is a kind of array. Just leave the [] and it should work

Answer 2

Actually what u did is also not wrong your declaration is right . With your declaration JVM will create a ArrayList of integer arrays i.e each entry in arraylist correspond to an integer array hence your add function should pass a integer array as a parameter.

For Ex:

list.add(new Integer[3]);

In this way first entry of ArrayList is an integer array which can hold at max 3 values.

Answer 3

The [] makes no sense in the moment of making an ArrayList of Integers because I imagine you just want to add Integer values. Just use

List<Integer> list = new ArrayList<>();

to create the ArrayList and it will work.

Answer 4

You are trying to add an integer into an ArrayList that takes an array of integers Integer[]. It should be

ArrayList<Integer> list = new ArrayList<>();

or better

List<Integer> list = new ArrayList<>();

Answer 5

How about creating an ArrayList of a set amount of Integers?

The below method returns an ArrayList of a set amount of Integers.

public static ArrayList<Integer> createRandomList(int sizeParameter)
{
    // An ArrayList that method returns
    ArrayList<Integer> setIntegerList = new ArrayList<Integer>(sizeParameter);
    // Random Object helper
    Random randomHelper = new Random();
    
    for (int x = 0; x < sizeParameter; x++)
    {
        setIntegerList.add(randomHelper.nextInt());
    }   // End of the for loop
    
    return setIntegerList;
}

Answer 6

List of Integer.

List<Integer> list = new ArrayList<>();
int x = 5;
list.add(x);