Question

I have a String data type adjacency matrix in Java:

String[][] A;

I want to read my adjacency matrix A into a MySQL table. The problem is I never know how many rows/columns I will need (nor would I want to create all the columns either). I think the trick to solving this problem is creating columns on the fly. How do I add columns “on the fly?”

Once I can add columns on the fly, I could then read in the matrix row by row.

1. I want to be able to view the data as a matrix.

All help is greatly appreciated!

Answer 1

Instead of going through the trouble of setting up variable columns, create a simple database table A:

row     integer
col     integer
content varchar

This gives you the flexibility to easily avoid empty entries and you have one database table row for every array item.

You have two options:

1. Generate one database row for every element of your array including nulls, or
2. Generate one database row for every element that is not null.

For option 1, this code will provide any element:

private String getElement(int row, int col) {
    String result = null;
    try {
        if(rs.absolute(row*colNumber+col+1))
            result=rs.getString("content");
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }
    return result;
}

For option 2, the content of the requested element at row,col is found like this:

private String getElement(int row, int col) {
    String result = null;
    String query = "SELECT * from A where row=? and col=?";
    try {
        PreparedStatement preps = con.prepareStatement(query);
        preps.setInt(1, row);
        preps.setInt(2, col);
        preps.execute();
        rs = preps.getResultSet();
        if (rs.next()) {
            result = rs.getString("content");
        }
    } catch (SQLException ex) {
        System.out.println(ex.getMessage());
    }

    return result;
}

It is obvious that option 1 is accessing elements faster. Option 2 saves database space.

PS: If you have an array of arrays of varying length option 1 will not work.
colNumber is the fixed number of columns of your String array.