CODEWITHSUNDEEP
javaarrays
user1692517
user1692517

Reputation: 1152

Java ArrayList for integers

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;

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

But I'm unable to add anything to the ArrayList using this method. It works if I use Strings for the array list. Would I have to make it a String array and then somehow convert the array to integers?

EDIT: I have another question. I'd like the list to only hold 3 values. How would I do so?

Upvotes: 25

Views: 221888

Answers (8)

Ivan
Ivan

Reputation: 427

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;
}

Upvotes: 0

Java-Dev
Java-Dev

Reputation: 458

Here there are two different concepts that are merged togather in your question.

First : Add Integer array into List. Code is as follows.

List<Integer[]> list = new ArrayList<>();
Integer[] intArray1 = new Integer[] {2, 4};
Integer[] intArray2 = new Integer[] {2, 5};
Integer[] intArray3 = new Integer[] {3, 3};
Collections.addAll(list, intArray1, intArray2, intArray3);

Second : Add integer value in list.

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

Upvotes: 1

David
David

Reputation: 175

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.

Upvotes: 1

Arjun Chaudhary
Arjun Chaudhary

Reputation: 2453

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.

Upvotes: 1

ylnsagar
ylnsagar

Reputation: 644

you are not creating an arraylist for integers, but you are trying to create an arraylist for arrays of integers.

so if you want your code to work just put.

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

Upvotes: 3

Subhrajyoti Majumder
Subhrajyoti Majumder

Reputation: 41200

List of Integer. 

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

Upvotes: 64

vishal_aim
vishal_aim

Reputation: 7854

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

Upvotes: 1

Jeff Storey
Jeff Storey

Reputation: 57192

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<>();

Upvotes: 7

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