Not sure about Array size

Question

How may I define an array in Java. when I am not sure of the Arrays size. I am doing it to avoid Null Pointers

int[] arr1 = new int[21];
int[] arr1 = {11,22,33};

These are of fixed length, i need to declare an Array where the items to be stored in it will be decided at run time?

http://stackoverflow.com/questions/1647260/java-dynamic-array-sizes — Anas Alkhatib, Nov 07 '14 at 15:26

score 2 · Answer 1 · answered Nov 07 '14 at 15:26

2

You could use an ArrayList, which dynamically grows/shrinks according to how many elements you place/remove in it.

http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html

answered Nov 07 '14 at 15:26

breen

4,282
5
19
32

Lucas · Answer 2 · 2014-11-07T15:37:24.577

1

if you are not sure just declare it like this:

int[] arr1;

but you must know its size when you initialise it later:

arr1 = int[20];
//or
arr1 = {1, 2, 3};

On the other hand this is the situation where you should use List (like ArrayList) since they resize dynamically.

EDIT:

 List<Integer> list = new ArrayList<Integer>(); 
 //adding 
 list.add(2);

more methods here: http://docs.oracle.com/javase/7/docs/api/java/util/List.html

edited Nov 07 '14 at 15:37

answered Nov 07 '14 at 15:26

Lucas

3,051
4
23
43

1

I think he means initialising an array without knowing the size. But yeah you are right. – ssayyed Nov 07 '14 at 15:32
Yes, seems right. I have never used ArrayList, reading about it. Can you give me the best way to declare/initialise it? – user3833732 Nov 07 '14 at 15:33
see my edit (I explained how to use it) – Lucas Nov 07 '14 at 15:37
Very Nice! worked it today. went off very well – user3833732 Nov 08 '14 at 14:23

score 0 · Accepted Answer · answered Nov 07 '14 at 15:27

0

"Array lists are created with an initial size. When this size is exceeded, the collection is automatically enlarged. When objects are removed, the array may be shrunk."

ArrayList Tutorial

answered Nov 07 '14 at 15:27

Harry

2,781
5
36
60

Not sure about Array size

3 Answers3