Problems with indexOf reading from an updating string

Question

String[][] shapeArray = new String[5][2];
int isCol;
int isCom;
String outputsub1 = finoutput;  // finoutput is holding text imported from a file
String outputsub2;
for (int y = 0; y < 2; y++)
     for (int x = 0; x < 5; x++)
          isCol = outputsub1.indexOf(":");
               isCom = outputsub1.indexOf(",");
              if (x == 4 && y == 1)
               shapeArray[x][y] = outputsub1.substring((isCol+2));
          else
                   shapeArray[x][y] = outputsub1.substring((isCol+2),isCom);
              outputsub2 = outputsub1.substring(isCom+2);
              outputsub1 = (outputsub2);
}the text imported looks like this...
Shape: Circle, Position: 100, 250, Size: 130, 130, Colour: Blue, Fill: yes
Shape: Rectangle, Position: 300, 250, Size: 110, 110, Colour: Red, Fill: no
i would use a string tokeniser, but i need to use this method. im trying to shorten the string each time so that the indexOf will find the next ":" each time. However when i try and update the string holding the updated data (outputsub1) i get the following error:
java.lang.StringindexOutOfBoundsException: String index out of range: -8
at java.lang.String.substring(String.java:144)
at ReadFile.init(ReadFile.java:52)
at sun.applet.AppletPanel.run(AppletPanel.java:353)
at java.lang.Thread.run(Thread.java:534)
i hope that makes sense to someone, it only occurs when i add the line..
outputsub1 = (outputsub2);
and works fine when i comment it out (although doesnt give the right response obviously.)
thankyou for any help you can offer

Answer 1

String index out of range: -8 simply means that you try to access the String at position "-8", which obviously makes no sense. There must be some mistake either in your code or your algorithm. Keep in mind that indexOf returns -1 in case the argument wasn't found - maybe that's the reason for that error.