Java - ArrayList Output

Question

I created an arraylist in Java called rows. Now I have a text file which contains information regarding a program (for example: DRAMA-Film A-2.5hours-hi) which is put into a string called strLine. strLine is then split and put into the arraylist rows.

Can anyone tell me why nothing is being output with the system.out.println statement?

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


class Processing
{
 public static void main(String args[])
  {
  try{

  FileInputStream fstream = new FileInputStream("file.txt");

  DataInputStream in = new DataInputStream(fstream);
  BufferedReader br = new BufferedReader(new InputStreamReader(in));
  String strLine = null;

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

    while ((strLine = br.readLine()) != null)   {


        String[] row = strLine.split("-");
        rows.add(row);

  }
  System.out.println(rows.toString());

  in.close();
    }catch (Exception e){
  System.err.println("Error: " + e.getMessage());
  }
  }
}

Answer 1

Your code is printing out the default representation of an array list. The symbols you are seeing output are the String array references that you are storing in this list. If you want more detailed output then you will need to code for it.

for(final String[] row: rows) {
    System.out.println(Arrays.toString(row);
}

As an example.

Answer 2

You can't just print an array, you need to print the parts of it.

for (String[] row : rows)
{
  for (String part : row)
    System.out.print(part + " ");
  System.out.println();
}

Answer 3

The default toString() method generates an internal string that represents the unique object. If you want to print a formatted string of the array contents, you can do this:

for (String[] row : rows) {
    System.out.println(Arrays.toString(row));
}

Answer 4

You're trying to print out an array of String and are expecting it to look like a string.

  System.out.println(rows.toString());

When you call that, by default it prints out every element in the list, but each element, as you've programmed it is an instance of String[], not String. You need to go a step deeper, inception style to get the results you expect.

Try adding a method like so:

    public static void print(List<String[]> list) {

     for(String[] arr : list) {
         StringBuffer buff = new StringBuffer();
         for(int i = 0; i < arr.length; i++) {
             buff.append(arr[i]);
         }
         System.out.println(buff.toString());
     } 
 }

and then call print(rows);

Answer 5

The ArrayList implementation of toString() prints the list using the toString() implementation of its elements. Array objects' implementation of toString() doesn't print the array contents; instead, you need to use Arrays.toString(). So you can either iterate over the list and print each array separately (see Ted Hopp's and Perception's answers), or if you really want to print it all in one go you can implement your own print method, something like this:

<T> String collectionOfArrsToString(Collection<T[]> collection) {
    // Adapted from AbstractCollection.toString() implementation
    Iterator<T[]> i = collection.iterator();
    if (!i.hasNext())
        return "[]";

    StringBuilder sb = new StringBuilder();
    sb.append('[');
    for (;;) {
        T[] tArr = i.next();
        sb.append(Arrays.toString(tArr));
        if (!i.hasNext())
            return sb.append(']').toString();
        sb.append(", ");
    }
}