How do I reference a specific index of element in an ArrayList?

Question

Let's say I initialize an ArrayList using the following code:

 ArrayList fib = new ArrayList();

    fib.add(18);
    fib.add(23);
    fib.add(37);
    fib.add(45);
    fib.add(50);
    fib.add(67);
    fib.add(38);
    fib.add(88);
    fib.add(91);
    fib.add(10);

What if I want to reference a specific index of the array. I don't want what's in the index. I want the index itself. I know this seems redundant, but it spills into another code.

To reference what's IN the index, I would do this:

 fib.temp(4);

and it would yield

What if I want what index it is?

Given the fact that List is 0 indexed, wouldn't it return 50...? — MadProgrammer
– MadProgrammer, Commented Jan 30, 2014 at 5:42
Your question is very inconsistent, using temp and fib almost interchangably - and then referring to your list as an array, which it certainly isn't... A lot of the discipline of software engineering is paying attention to the details. Please take more care in your next question. — Jon Skeet
– Jon Skeet, Commented Jan 30, 2014 at 5:44
You are mixing up ArrayList with Array, what you want, Array can do that for you... — Not a bug
– Not a bug, Commented Jan 30, 2014 at 6:23
Apologies, everyone. This question was posted in a rush. I'm usually very considerate of my writing. Thank you for your edits, answers, and comments. — priya
– priya, Commented Jan 30, 2014 at 6:45

Jon Skeet · Accepted Answer · 2014-01-30 05:41:42Z

3

I suspect you're looking for List.indexOf:

int index = fib.indexOf(45); // index is now 3

indexOf returns -1 if the value isn't found in the list.

Note that temp isn't a member of ArrayList, and if you use fib.get(4) it will return 50, not 45 - because the index is 0-based, not 1-based.

answered Jan 30, 2014 at 5:41

Jon Skeet

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5 Comments

priya Over a year ago

So it would be temp.indexOf(4)? And that would return...4?

MadProgrammer Over a year ago

@priya No, it would return -1 based on the example. temp.indexOf(50) would return 4...

Jon Skeet Over a year ago

@priya: No, it would be temp.indexOf(45). Or maybe fib.indexOf(45) - the naming in your question is inconsistent. Either way, that would return 3.

priya Over a year ago

@JonSkeet That makes sense. I feel foolish for forgetting counting starts at 0. Thanks.

priya Over a year ago

And yes - I mixed up the ArrayList names. It should be: ArrayList fib = new ArrayList();

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