Java 2D ArrayList

Question

so every time i run the program and enter the 2nd choice, it tells me rangecheck error , index0 , size 0.

what i understand from this after research is that the arraylist is empty, how do i use the add function in the 2D arraylist?

|ABCDEFGHIJKLMNOPQRSTUVWX

--+------------------------

01|gggggggggggggggggggggggg

02|gGGGGGGGGGGGGGGGGGGGGGGg

03|gGggggggggggggggggggggGg

04|gGgYYYYYYYYYYYYYYYYYYgGg

05|gGgYggggggggggggggggYgGg

06|gGgYggggggggggggggggYgGg

07|gGgYggYYYYYYYYYYYYggYgGg

08|gGgYggYggggggggggYggYgGg

09|gGgYYYYggggggggggYYYYgGg

10|gGggggggggggggggggggggGg

11|gGGGGGGGGGGGGGGGGGGGGGGg

12|gggggggggggggggggggggggg

package map;
import java.io.FileInputStream;
import java.io.InputStream;
import java.util.Scanner;
import java.util.ArrayList;

public class MapMain 
{
    public static void main(String [ ] args)
    {
        Scanner input = new Scanner(System.in);
        InputStream is = null;
          int i;
          char c;
          String T;
          ArrayList<ArrayList<String>> Contain = new ArrayList<ArrayList<String>>();
          for(int L = 0; L < 30; L++)
          {
              Contain.add(new ArrayList<String>());
          }

          try{
              do{
            int a=0;
            String Elements;
            System.out.print("To load map enter 1\nTo print loded map enter 2\nTo change specific elements press 3  ");
            a=input.nextInt();
            switch (a){
            case 1 :
                System.out.print("What is the file dest?");
                T=input.nextLine();
                is = new FileInputStream(T);
                while((i=is.read())!=-1)
                {
                   c=(char)i;
                   String O = "ankosh";
                   //Contain.add(Contain.O);
                }
                break; 
            case 2:
                while(true)
                {
                   String U = Contain.get(16).get(0);
                   //System.out.print(Contain);
                   break;
                }
                break;
            case 3:
                System.out.print("What do you want to insert?");
                Elements=input.nextLine();
                //switch (Elements){
                //case 
                }
                break;
            } while(true);
          }catch(Exception e){

        // if any I/O error occurs
        e.printStackTrace();
     }finally{
     }
    }
}

Answer 1

You created the array of arrays, and the arrays it contains, so far it's ok. Now, on case 2 you are trying to reach the first element of the 16th array (basically of type String) which is null since you didn't add anything yet to this array. What you need to do before trying the get(index), is to check that the length of the array is bigger than the index. In order to add to the array:content.get(16).add(str);.