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   ArrayList lt Integer   gt  list   new ArrayList lt  gt     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

User · Answer

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);

User · Answer

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 lt Integer gt  list   new ArrayList lt  gt     int x   5  list add x

User · Answer

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

User · Answer

You are trying to add an integer into an ArrayList that takes an array of integers Integer    It should be  ArrayList lt Integer gt  list   new ArrayList lt  gt       or better  List lt Integer gt  list   new ArrayList lt  gt

User · Answer

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 lt Integer gt  list   new ArrayList lt  gt       to create the ArrayList and it will work

User · Answer

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

User · Answer

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 lt Integer gt  createRandomList int sizeParameter           An ArrayList that method returns     ArrayList lt Integer gt  setIntegerList   new ArrayList lt Integer gt  sizeParameter          Random Object helper     Random randomHelper   new Random             for  int x   0  x  lt  sizeParameter  x                  setIntegerList add randomHelper nextInt                End of the for loop          return setIntegerList

User · Answer

List of Integer    List lt Integer gt  list   new ArrayList lt  gt     int x   5  list add x

[java] Java ArrayList for integers

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