Java : Resizing a multidimensional array

Question

I have a multidimensional array built from Strings that is initially created with the size [50][50], this is too big and now the array is full of null values, I am currently trying to remove these said null values, I have managed to resize the array to [requiredSize][50] but cannot shrink it any further, could anyone help me with this? I have scoured the internet for such an answer but cannot find it.

Here is my complete code too (I realise there may be some very unclean parts in my code, I am yet to clean anything up)

import java.io.*;
import java.util.*;

public class FooBar
{
  public static String[][] loadCSV()
  {
    FileInputStream inStream;
    InputStreamReader inFile;
    BufferedReader br;
    String line;
    int lineNum, tokNum, ii, jj;
    String [][] CSV, TempArray, TempArray2;

    lineNum = tokNum = ii = jj  = 0;
    TempArray = new String[50][50];

    try
    {
        BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Please enter the file path of the CSV");
        String fileName = in.readLine();
        inStream = new FileInputStream(fileName);
        inFile = new InputStreamReader(inStream);
        br = new BufferedReader(inFile);
        StringTokenizer tok,tok2;


        lineNum = 0;
            line = br.readLine();
            tokNum = 0;
            tok = new StringTokenizer(line, ",");

            while( tok.hasMoreTokens())
            {
                TempArray[tokNum][0] = tok.nextToken();
                tokNum++;
            }
            tokNum = 0;
            lineNum++;

            while( line != null)
            {
                    line = br.readLine();
                    if (line != null)
                    {
                        tokNum = 0;
                        tok2 = new StringTokenizer(line, ",");

                        while(tok2.hasMoreTokens())
                        {
                            TempArray[tokNum][lineNum] = tok2.nextToken();
                            tokNum++;
                        }
                    }
                    lineNum++;
            }
    }    
    catch(IOException e)
    {
        System.out.println("Error file  may not be accessible, check the path and try again");
    }

    CSV = new String[tokNum][50];
    for (ii=0; ii<tokNum-1 ;ii++)
    {
        System.arraycopy(TempArray[ii],0,CSV[ii],0,TempArray[ii].length);
    }
    return CSV;
}    
public static void main (String args[])
{
    String [][] CSV;
    CSV = loadCSV();
    System.out.println(Arrays.deepToString(CSV));
}
}                

The CSV file looks as follows

Height,Weight,Age,TER,Salary
163.9,46.8,37,72.6,53010.68
191.3,91.4,32,92.2,66068.51
166.5,51.1,27,77.6,42724.34
156.3,55.7,21,81.1,50531.91

It can take any size obviously but this is just a sample file.

I just need to resize the array so that it will not contain any null values.

I also understand a list would be a better option here but it is not possible due to outside constraints. It can only be an multi dimensional array.

Answer 1

Here's an observation and a suggestion.

Observation: Working with (multidimensional) arrays is difficult in Java.

Suggestion: Don't use arrays to represent complex data types in Java.

Create classes for your data. Create a List of people:

class Person {
    String height;  //should eventually be changed to a double probably
    String weight;  // "
    //...

    public Person( String height, String weight /*, ... */ ) {
       this.height = height;
       this.weight = weight;
       //...
    }
}

List<Person> people = new ArrayList<Person>();
String line;
while ( (line = reader.nextLine()) != null ) {
    String[] records = line.split(",");
    people.add(new Person (records[0], records[1] /*, ... */));
}

Answer 2

10 to 1 this is a homework assignment. However, it looks like you've put somethought into it.

Don't make the TempArray variable. Make a "List of List of Strings". Something like:

List<List<String>> rows = new ArrayList<ArrayList<String>>();

while(file.hasMoreRows()) {            //not valid syntax...but you get the jist
  String rowIText = file.nextRow();    //not valid syntax...but you get the jist
  List<String> rowI = new ArrayList<String>(); 

  //parse rowIText to build rowI --> this is your homework

  rows.add(rowI);

}

//now build String[][] using fully constructed rows variable

Answer 3

I think you need 3 changes to your program

• After your while loop lineNum will be 1 more than the number of lines in the file so instead of declaring CSV to String[tokNum][50] declare it as CSV = new String[tokNum][lineNum-1];
• tokNum will be the number of fields in a row so your for loop condition should be ii<tokNum rather than ii<tokNum-1
• The last parameter for your arraycopy should be lineNum-1

i.e. the modified code to build your CSV array is:

CSV = new String[tokNum][lineNum-1];
for (ii=0; ii<tokNum ;ii++)
{
    System.arraycopy(TempArray[ii],0,CSV[ii],0,lineNum-1);
}

and the output will then be:

[[Height, 163.9, 191.3, 166.5, 156.3], [Weight, 46.8, 91.4, 51.1, 55.7], 
[Age, 37, 32, 27, 21], [TER, 72.6, 92.2, 77.6, 81.1],
[Salary, 53010.68, 66068.51, 42724.34, 50531.91]]

Notice that you don't really need to handle the first line of the file separately from the others but that is something you can cover as part of your cleanup.