initialize two dimensional string array with dynamic size in java

Question

I have unknown number of records and I need to put all that records in string two dimensional array.

I don't know the number of records and due to this, don't know number of rows and columns which is required for string 2d array initialization.

Currently I am using as below:

String[][] data = new String[100][100]; 

Here I hard coded number of rows and columns but need something dynamic size allowable in string 2d array. Any suggestion pls!

Rgrds

Answer 1

You can use the following class which stores your data in a HashMap and is able to convert it to a two dimensional string array.

public class ArrayStructure {
    private HashMap<Point, String> map = new HashMap<Point, String>();
    private int maxRow = 0;
    private int maxColumn = 0;

    public ArrayStructure() {
    }

    public void add(int row, int column, String string) {
        map.put(new Point(row, column), string);
        maxRow = Math.max(row, maxRow);
        maxColumn = Math.max(column, maxColumn);
    }

    public String[][] toArray() {
        String[][] result = new String[maxRow + 1][maxColumn + 1];
        for (int row = 0; row <= maxRow; ++row)
            for (int column = 0; column <= maxColumn; ++column) {
                Point p = new Point(row, column);
                result[row][column] = map.containsKey(p) ? map.get(p) : "";
            }
        return result;
    }
}

Example code

public static void main(String[] args) throws IOException {
    ArrayStructure s = new ArrayStructure();
    s.add(0, 0, "1");
    s.add(1, 1, "4");

    String[][] data = s.toArray();
    for (int i = 0; i < data.length; ++i) {
        for (int j = 0; j < data[i].length; ++j)
            System.out.print(data[i][j] + " ");
        System.out.println();
    }
}

Output

1  
 4 

Answer 2

You can temporarely store them in a List<String[]> and use List#toArray(String[]) to convert it to a two dimensional array.

Example

public static void main(String[] args) throws IOException {
    BufferedReader r = new BufferedReader(new FileReader(new File(
            "data.txt")));

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

    while ((line = r.readLine()) != null)
        list.add(line.split(" +"));

    String[][] data = new String[list.size()][];
    list.toArray(data);

    for (int i = 0; i < data.length; ++i) {
        for (int j = 0; j < data[i].length; ++j)
            System.out.print(data[i][j]+" ");
        System.out.println();
    }
    r.close();
}

Data.txt

1 2 3 4 5
2 5 3
2  5  5 8

Output

1 2 3 4 5
2 5 3
2 5 5 8

Answer 3

您可以简单地使用文字，空的二维数组进行初始化：

String[][] data = new String[][]{{}}

Answer 4

This should work:

public static void main(String args[]) throws IOException {
    // create the object
    String[][] data;

    // ----- dinamically know the matrix dimension ----- //
    BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
    int r = Integer.parseInt(bufferedReader.readLine());
    int c = Integer.parseInt(bufferedReader.readLine());
    // ------------------------------------------------ //

    // allocate the object
    data = new String[r][c];

    // init the object
    for (int i = 0; i < r; i++)
        for (int j = 0; j < c; j++)
            data[i][j] = "hello";
}

In this example you know the matrix dimension runtime, specifying it manually via the console.