Parse input in java from mutiple line

Question

I have got n lines of numbers , all containing equal number of numbers lets say m , how to store them in 2d array

1 5 7 9  
2 3 4 6  
3 4 5 8

Note that here value of n and m is not given .

    BufferedReader br = new BufferedReader (new     InputStreamReader(System.in));
    Scanner sc=new Scanner(System.in);
    while(sc.hasNextLine())
    {
    String line=br.readLine();
    String [] str =line.trim().split(" ");
    int n=str.length;
    columns=n;
    for(int i=0;i<n;i++)
    {
        matrix[rows][i]=Integer.parseInt(str[i]);
    }
        rows++;
    }

Runtime error is coming
Runtime error time: 0.14 memory: 321088 signal:-1

please post the code you have already tried yourself to achieve this, then post any errors/problems you have with that code. — BMac
– BMac, Commented Apr 15, 2015 at 8:02
If you don't know the number of items and you already need to store it, you can use an implementation of List, like ArrayList to store, at least while you're loading the data. You can convert it to an array later with the toArray method. — Erwin Bolwidt
– Erwin Bolwidt, Commented Apr 15, 2015 at 8:06

Tim Biegeleisen · Accepted Answer · 2015-04-15 08:26:50Z

2

You can temporarily store everything into an ArrayList, then iterate over it at the end and create your 2D array:

BufferedReader br = new BufferedReader("C:/YourFile.txt");
ArrayList<Integer> list = new ArrayList<Integer>();
int rows=0, cols=0;
String line;
while ((line = br.readLine()) != null) {
    String [] str = line.trim().split(" ");
    int n = str.length;
    cols = n;
    for (int i=0; i < n; ++i) {
        list.add(Integer.parseInt(str[i]));
    }
    ++rows;
}

// now create a 2D array and store everything into it
int[][] array = new array[rows][cols];
for (int i=0; i < rows; ++i) {
    for (int j=0; j < cols; ++j) {
        array[i][j] = list.get(i*cols+j);
    }
}

edited Apr 15, 2015 at 8:26

answered Apr 15, 2015 at 8:11

Tim Biegeleisen

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6 Comments

user3529205 Over a year ago

its should be list.add(Integer.parseInt(str[i]) still runtime error is coming

Tim Biegeleisen Over a year ago

Good catch...I don't have access to a JVM at the moment ^ ^

user3529205 Over a year ago

while(sc.hasNextLine()) { String line = br.readLine(); System.out.println(line); // here null is printed String [] str = line.trim().split(" ");

Tim Biegeleisen Over a year ago

What do you mean by your comment?

user3529205 Over a year ago

if i am printing line read by br , null is printed instead of line read

|

user1907906 · Accepted Answer · 2015-04-15 08:06:53Z

1

Try this:

    List<List<Integer>> ints = new ArrayList<>();
    String d = "1 5 7 9  \n"
            + "2 3 4 6  \n"
            + "3 4 5 8  ";
    for (String line : d.split("\n")) {
        List<Integer> row = new ArrayList<>();
        for (String cell : line.split(" ")) {
            row.add(Integer.parseInt(cell));
        }
        ints.add(row);
    }
    System.out.println(ints);

Output:

[[1, 5, 7, 9], [2, 3, 4, 6], [3, 4, 5, 8]]

answered Apr 15, 2015 at 8:06

user1907906

Comments

Community · Accepted Answer · 2017-05-23 11:57:03Z

1

Not sure, but I think using System.in in two objects (Scanner and InputStreamReader) causes issues, as characters may be consumed by the scanner before being read by the reader.

If you leave away the scanner, and just use BufferedReader.ready() in your while condition, it works (nearly the same code) :

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
while(br.ready())
{
    String line=br.readLine();
    String [] str =line.trim().split(" ");
    int n=str.length;
    columns=n;
    for(int i=0;i<n;i++)
    {
        matrix[rows][i]=Integer.parseInt(str[i]);
    }
    rows++;
}

You might prefer Tichodroma's more elegent answer.

edited May 23, 2017 at 11:57

CommunityBot

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answered Apr 15, 2015 at 8:21

superbob

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1 Comment

superbob Over a year ago

I suggest an answer that is closer to the OP initial attempt, however I personally prefer Tichodroma's answer

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