将2D String数组转换为2D double

Question

I'm a bit confused right now. I made this function to rewrite my 2D String array into a 2D double array. But it's casting nullpointer exceptions. The data in d2 is in the format : String[i][0/1] where 0 and 1 is a number in the format "0.3343434".

  public void StringToDouble () {
     unsorted = new double[d2.length][2];

     for(int i = 0; i < d2.length; i++)
    {
        unsorted[i][0] = Double.parseDouble(d2[i][0]);    
        unsorted[i][1] = Double.parseDouble(d2[i][1]);
    }

}

I'm getting an error when i print unsorted[0][0] and [1][1].

Here is the whole code.

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.Scanner;


public class LoadAndSort {

String raw;
double [][] data;
String [] datastring;

// 2D CONVERT

String [] d1;
String [][] d2;
double[][] unsorted;
double [][] sorted;
String path = "src/data.dat";


 public LoadAndSort () throws IOException {



    // # Reads file from disk and stores to variable.
    datas = readFile(path);
    // # Splits the content, and sorts it into a huge string with relevant variables.

    // # Splits on newline to order the lines.
    d1 = datas.split("\\r?\\n");
    // # Splits on comma to convert to 2D Array. 
    Convert2D();
    // # Mirrors the 2D array because Mikal is gay.
    //MirrorArray();
    //StringToDouble();

    System.out.println(unsorted[0][0]);
    System.out.println(unsorted[0][1]);

}



private static String readFile(String path) throws IOException {
    FileInputStream stream = new FileInputStream(new File(path));
    try {
        FileChannel fc = stream.getChannel();
        MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0, fc.size());
        /* Instead of using default, pass in a decoder. */

        return Charset.defaultCharset().decode(bb).toString();
    }
    finally {
        stream.close();
    }
}

public void Convert2D () {

    d2 = new String[d1.length][]; 
    int r = 0;
    for (String row : d1) {
        d2[r++] = row.split(",");
    }
}

public void StringToDouble () {

    unsorted = new double[d2.length][2];


    for(int i = 0; i < d2.length; i++)
    {
        unsorted[i][0] = Double.parseDouble(d2[i][0]);
        System.out.println(d2[i][0]);

        unsorted[i][1] = Double.parseDouble(d2[i][1]);
    }

}


}

And the error from console :

 0.00965821033009
 Exception in thread "main" java.lang.NullPointerException
at LoadAndSort.<init>(LoadAndSort.java:48)
at Runner.main(Runner.java:13)

Answer 1

You initialize unsorted in StringToDouble (with unsorted = new double[d2.length][2]; ), but the function call in the constructor is currently commented out, so unsorted will never be initialized.

Thus it will be null and a NullPointerException will be thrown here:

System.out.println(unsorted[0][0]);

Not sure whether this is the only problem, but first things first.

Answer 2

You can also use Streams API from Java 8

Double[][] c = Arrays.stream(stringArray).map(
                a -> Arrays.stream(a).map(
                        b -> Double.valueOf(b)
                        ).toArray(Double[]::new)
                ).toArray(Double[][]::new);