Splitting string[] to ArrayList and Returning Values

Question

I'm having an issue splitting a string array into a List/ArrayList. I realise this is basic stuff but I've looked at so many examples that I've now completely confused myself at what's happening (or not happening).

Some code snippets:

private String[] stringTempList;
private ArrayList<List<String>> arrayImageList = new ArrayList<List<String>>();

My list is read from a webpage and is formatted in plain text like: ['One','Two','Three', etc ...]

So, some lines to strip out the stuff I want/don't want (note - I've separated these out to help me follow the process through):

stringExtractedList = stringText.substring(stringText.indexOf("['") + 2,
                stringText.lastIndexOf("']"));    
stringTempList = stringExtractedList.split("','");

From what I can see the above works as expected (creating an array (stringTempList), splitting out each item where it sees ','.

Where it's going wrong:

arrayImageList.add((List<String>) Arrays.asList(stringTempList));

I expect this line to take my array (stringTempList) and move the items into an ArrayList. I was hoping to use code similar to arrayImageList.get(i); to access individual elements.

However, the code above seems to add all items to the first index in arrayImageList (list size is always 1). Running some debug tests eg Log.d("Test", arrayImageList.get(0)); returns the following:

[One,Two,Three,Four, etc...]

I'd be grateful if someone could point me in the right direction. I think I've confused two different ideas here.

Not familiar with Java, but private ArrayList<List<String>> arrayImageList = new ArrayList<List<String>>(); creates a list of lists. What you want is a list only. So pick either ArrayList or List<String>. At that point it is redundant to create a new list - so just take the result of split directly. Or convert it to the desired type (most likely creating a copy in that step) — skarmats
– skarmats, Commented May 21, 2012 at 19:30
Do you want to create lists of lists with parsed elements from the string? arrayImageList.add((List<String>) Arrays.asList(stringTempList)); is not valid java code. — Maarten Blokker
– Maarten Blokker, Commented May 21, 2012 at 19:34

krock · Accepted Answer · 2012-05-21 19:32:50Z

2

Change arrayImageList to a list of strings:

private ArrayList<String> arrayImageList = new ArrayList<String>();

and add them using the addAll method:

arrayImageList.addAll((List<String>) Arrays.asList(stringTempList));

answered May 21, 2012 at 19:32

krock

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1 Comment

tw332 Over a year ago

Thank you. In my error correcting previous errors, I stumbled on the ArrayList<List<String>> solution which just confused me. Simple solution here.

ametren · Accepted Answer · 2012-05-21 19:35:24Z

2

I think you want to use addAll() instead of add()

You'll also want to declare

private List<String> arrayImageList = new ArrayList<String>();

edited May 21, 2012 at 19:35

answered May 21, 2012 at 19:30

ametren

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2 Comments

ametren Over a year ago

No problem! Does the reasoning behind this make sense to you?

tw332 Over a year ago

Yeah, I think so. I'm very new to Java (and OOP in general) so applying my previous coding knowledge doesn't always help. In my research (trying to debug my issue) I found that an ArrayList is an implementation of a List. I also read that List should be used in preference of ArrayList where possible. In my case - initially I expected the array to be fixed length (so List would have done) but as I plan further - I suspect a non-fixed length list is going to be beneficial (eg removing broken image links).

Keith Randall · Accepted Answer · 2012-05-21 19:30:07Z

1

You want to use addAll, not add.

answered May 21, 2012 at 19:30

Keith Randall

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1 Comment

tw332 Over a year ago

Thanks. I think part of the confusion was that .add seemed to be adding all the elements - just not as expected.

Julian · Accepted Answer · 2012-05-21 19:38:56Z

0

I'm not sure i got this "wrong the right way", and I'm not that familiar with java, but here are my thoughts:

Your "arrayImageList" object is an ArrayList of List's. When youre adding your stringTempList-object, that object is correctly stored at the first available index of your 'List-of-lists'. If you want to access the individual elements (strings) from your "arrayImageList", you either have to adress the second dimension (the list of the list) like this:

arrayImageList.get(0).get(i) <- not entirely sure about java-syntax here, but you get the picture.

If on the other hand you dont need the extra dimension, just use ArrayList instead og ArrayList>.

answered May 21, 2012 at 19:38

Julian

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