Java ArrayList Casting Issue

Question

I have an ArrayList in Java which is full of int's. I am accessing it through get method. Now, I need array list int objects as ints to perform some operations. So, what I am doing is,

int i = Integer.parseInt(arraylist.get(position).toString()) + 100 ...

Is there any-other nice way to do it (means efficiently) ?

"I have an ArrayList in Java which is full of int's". No, you don't. You can't store primitives in an ArrayList. You have an ArrayList of Integer objects. — Jesper
– Jesper, Commented May 1, 2012 at 10:09
@Jesper, Thanks. Sorry, I said it wrongly. I mean int objects. — Arpssss
– Arpssss, Commented May 1, 2012 at 13:48
No, you mean Integer objects. int is a primitive type; an int is not an object. — Jesper
– Jesper, Commented May 2, 2012 at 7:04

David · Accepted Answer · 2012-05-01 09:32:58Z

3

What version of Java are you using? Since Java 1.5 the 'autoboxing' feature should take care of this for you.

int i = arrayList.get(position) + 100;

answered May 1, 2012 at 9:32

David

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3 Comments

David Over a year ago

You haven't shown us where your array is instantiated. If you have it set up as an array of Integers this should work.

Arpssss Over a year ago

Ok sorry. I have not declared it as INT.

David Over a year ago

Ah, ok. I guess that was an assumption on my part.

Martinecko · Accepted Answer · 2012-05-01 09:33:08Z

3

Perhaps:

List<Integer> myList = new ArrayList<Integer>();
myList.put(1);
myList.put(2);
...
int num = myList.get(index) + 100;

Or do whatever you like, collection will contain only Integers so you don't have to convert it. Plus, autoboxing takes care for int->Integer and back.

answered May 1, 2012 at 9:33

Martinecko

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Comments

Jon Skeet · Accepted Answer · 2012-05-01 09:38:20Z

3

Yes - don't convert to a string and back!

int i = arrayList.get(position).intValue() + 100;

Or using auto-unboxing:

int i = arrayList.get(position) + 100;

As noted in comments, I'm happy with auto-unboxing when the expression is just used in assignment expression (or as a method argument) - when it's used as part of an arithmetic expression, I generally prefer to make it explicit.

(Note that your list will be full of Integer references, not int values.)

edited May 1, 2012 at 9:38

answered May 1, 2012 at 9:31

Jon Skeet

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3 Comments

Arpssss Over a year ago

Thanks a lot. Nice way to do.

Greg Kopff Over a year ago

With auto-unboxing, you can simplify it to int i = arrayList.get(position) + 100;

Jon Skeet Over a year ago

@GregKopff: While I suspected that would be okay, I wasn't 100% sure it would unbox as part of the arithmetic. I normally only use unboxing directly in assignment - I feel this ends up being clearer. Will add the option though.

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