Saving values inside while loop

Question

I am trying to read values of my country array string which reads csv file.

InputStreamReader reader = new InputStreamReader(asset_stream);  
br = new BufferedReader(reader);
String[] country = null;
String cvsSplitBy = ";";

try {
    while ((line = br.readLine()) != null) {
        country = line.split(cvsSplitBy);

    }
} catch (NumberFormatException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}

My code is currently storing the values inside the country variable. But when my loop finishes, I only have the last value read in the loop. How can I store all the values so I can print them after finishing the loop?

Can you use a `List`? Please post some sample data and expected output. — Elliott Frisch, Feb 03 '14 at 15:45
In your data, where are the countries: 1. in a column in every line or 2. all in a single line? If 1, then you must first get the column in every line. If 2, in which line are they and why to read all lines? — wolfrevo, Feb 03 '14 at 15:52

Duncan Jones · Answer 1 · 2014-02-03T15:53:01.507

7

Consider using a list to hold the values:

List<String[]> countries = new ArrayList<>();

try {
    while ((line = br.readLine()) != null) {
        countries.add(line.split(cvsSplitBy));    
    }
}

Later you can iterate over this list:

for (String[] country : countries) {
  System.out.println(Arrays.toString(country); // or whatever
}

edited Feb 03 '14 at 15:53

answered Feb 03 '14 at 15:47

Duncan Jones

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thanks a lot @Dunkun. that was quite quick and accurate reply . Works like charm.. – muktoshuvro Feb 03 '14 at 16:00
1

@muktoshuvro Then you should select his answer as a solution to your question. Although you could also pick [mine](http://stackoverflow.com/a/21531679/3239833) ;) – SebastianH Feb 03 '14 at 16:09

score 4 · Answer 2 · answered Feb 03 '14 at 15:51

Assuming you're reading multiple countries per line, you may be able to use something like this -

public static List<String> getCountryList(InputStream asset_stream) {
    InputStreamReader reader = new InputStreamReader(asset_stream);
    BufferedReader br = new BufferedReader(reader);
    String[] country = null;
    List<String> al = new ArrayList<String>();
    try {
        String line;
        while ((line = br.readLine()) != null) {
            country = line.split(cvsSplitBy);
            for (String s : country) {
                al.add(s);
            }
        }
    } catch (NumberFormatException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        br.close();
    }
    return al;
}

score 3 · Answer 3 · answered Feb 03 '14 at 15:49

3

With every loop your are splitting the current line and saving its parts in the country array. Therefore you can only see the results of your last line after the while loop.

If you want to store the splitted results of every line you should use a collection of String[]. For example like this:

LinkedList<String[]> list = new LinkedList<String[]>();
while ((line = br.readLine()) != null) {
    list.add(line.split(cvsSplitBy));
}
//To read values
for (String[] entry : list) {
    //do something with entry
}

answered Feb 03 '14 at 15:49

SebastianH

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Why a `LinkedList` out of interest? – Duncan Jones Feb 03 '14 at 15:57
2

Since we fill the List line by line and do not know how many elements will be added I expect LinkedList to be better suited than ArrayList (where the backing array has to be copied several times during the creation of the list). Of course it strongly depends on the later use of the List. Btw: I like how you used the List interface in the declaration in your answer, but again this can be a pain for the later use of the variable. – SebastianH Feb 03 '14 at 16:03
Good point regarding the unknown input size. I probably use `ArrayList` too often without considering exactly why. After reading your comment, I found [this SO question](http://stackoverflow.com/questions/322715/when-to-use-linkedlist-over-arraylist) which summarises things nicely. – Duncan Jones Feb 03 '14 at 16:06

Satyan Raina · Answer 4 · 2014-02-03T16:23:09.403

You can store them in one of the collection types. (see http://docs.oracle.com/javase/7/docs/api/java/util/Collection.html)

Java collections provide you various data structures to store and retrieve data in a particular order. For example, a List will allow you to retrieve the data by index and will preserve the insertion order (FIFO). Other data structures like trees, queues, stacks, sets have other properties.

Using a List in your code:


    InputStreamReader reader = new InputStreamReader(asset_stream);  
    br = new BufferedReader(reader);
    List &ltString[]> countries=new LinkedList &ltString[]>();

    try {
        while ((line = br.readLine()) != null) {
            countries.add(line.split(cvsSplitBy));
        }
    } catch (NumberFormatException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    for(String[] country: countries)
    {
      //Do something useful with your List
      System.Out.println(country[0]);
    }

why don't you use generics? Everytime you don't use generics a Coffee plant dies. — Martin Braun, Feb 03 '14 at 16:01
I HAVE used generics. SO is thinking it is a markup tag... Need to figure out how to escape it — Satyan Raina, Feb 03 '14 at 16:04

wolfrevo · Answer 5 · 2014-02-04T10:53:31.550

1

split returns a String-array which you assign to your array country. You should assign the result of split to a position in country, i.e. country[i]. If you do not use a List instead of your array, then you must dimensionate the array first! I.e. create it with a given size new String[size]

edited Feb 04 '14 at 10:53

answered Feb 03 '14 at 15:48

wolfrevo

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@Duncan `String[] country = new String[number_of_countries];` Arrays must have a lenght when created. – wolfrevo Feb 03 '14 at 15:56
Ok, gotcha. Not sure that's a real word, but I like it nonetheless :-) – Duncan Jones Feb 03 '14 at 15:57
You're right: it is not a real english word. I meant creating an array with a given length. – wolfrevo Feb 03 '14 at 16:01
You should of course use `List`. But you were asking why you only get the last value in your array? – wolfrevo Feb 03 '14 at 16:04

Saving values inside while loop

5 Answers5