Java Illegal Argument: n must be positive Please help

Question

hi guys. I have a program that creates random word squares that are true; meaning, it spells a word that exists in a text file of words in each column and row. I am getting a really annoying exception though.
sometimes i get
Error: java.lang.IllegalArgumentException: n must be positiveand someteimes i get
Error: java.lang.ArrayIndexOutOfBoundsException: 2where the number 2 is always the size of the square (strLength)
here is my code.
import java.io.*;
import java.util.*;
import javax.swing.*;
import java.lang.*;
class WordSquare
     public static void main(String[] args)
          String textFile,input,line,sWord="",goWord="";;
          int strLength,decision,testAvail=-1;
          textFile = "newwords.txt";
          input = JOptionPane.showInputDialog("How many characters would you like each word to be?");
          strLength = Integer.parseInt(input);
          input = JOptionPane.showInputDialog("Would you like to have a specific starting word?\n1. Yes\n2. No");
          decision = Integer.parseInt(input);
          try
               BufferedReader inputFile = new BufferedReader(new FileReader(textFile));
               ArrayList data = new ArrayList();
               line=inputFile.readLine();
               char[][] sq = new char[strLength][strLength];     
               while(line != null)
                    if(line.length()==strLength)
                         data.add(line);
                    line=inputFile.readLine();
               System.out.println("List contains " + data.size() + " " + strLength + "-letter words.");
               if(decision == 1)
                    sWord = JOptionPane.showInputDialog("Enter your desired " + strLength +"-letter word.");
                    String testPref = Character.toString(sWord.charAt(0));
                    testAvail = bSearchPref(data, testPref);
                    if(testAvail==-1)
                         System.out.println("Word square with provided word is not possible!");
               boolean completeSquare = false;
               while(completeSquare==false)
                    for(int m=0; m<strLength; m++)
                         for(int n=0; n<strLength; n++)
                              sq[m][n] = '*';
                    if(decision == 1)
                         if(testAvail==-1)
                              int rNumber = getRandom(0,data.size()-1);
                              goWord = (String)data.get(rNumber);
                              for(int k=0;k<strLength;k++)
                                   sq[0][k] = goWord.charAt(k);
                         else
                              for(int j=0;j<strLength;j++)
                                   sq[0][j] = sWord.charAt(j);
                    else
                         int rNumber = getRandom(0,data.size()-1);
                         goWord = (String)data.get(rNumber);
                         for(int q=0;q<strLength;q++)
                              sq[0][q] = goWord.charAt(q);
                    String prefix = Character.toString(sq[0][0]);
                    int prefIndex,first,last,randIndex;
                    prefIndex=bSearchPref(data,prefix);
                    first = getFirst(data,prefix,prefIndex);
                    last = getLast(data,prefix,prefIndex);
                    randIndex = getRandom(first,last);
                    goWord = (String)data.get(randIndex);
                    for(int z=0; z<strLength; z++)
                         sq[z][0] = goWord.charAt(z);
                    for(int a=1; a<strLength; a++)
                         int b=0;
                         prefix="";
                         while(sq[a]!='*' && b<strLength)
                              prefix += Character.toString(sq[a][b]);
                              b++;
                         prefIndex=bSearchPref(data,prefix);
                         if(prefIndex==-1)
                              a = strLength;
                         else
                              first = getFirst(data,prefix,prefIndex);
                              last = getLast(data,prefix,prefIndex);
                              randIndex = getRandom(first,last);
                              goWord = (String)data.get(randIndex);
                              for(int x=0; x<strLength; x++)
                                   sq[a][x] = goWord.charAt(x);
                              b=0;
                              prefix="";
                              while(sq[b][a]!='*' && b<strLength)
                                   prefix += Character.toString(sq[b][a]);
                                   b++;
                              prefIndex=bSearchPref(data,prefix);
                              if(prefIndex==-1)
                                   a = strLength;
                              else
                                   first = getFirst(data,prefix,prefIndex);
                                   last = getLast(data,prefix,prefIndex);
                                   randIndex = getRandom(first,last);
                                   goWord = (String)data.get(randIndex);
                                   for(int y=0; y<strLength; y++)
                                        sq[y][a] = goWord.charAt(y);
                    String testSquare="";
                    for(int h=0;h<strLength;h++)
                         testSquare += Character.toString(sq[h][strLength-1]);
                    int squareResult = bSearchFull(data, testSquare);
                    if(squareResult!=-1)
                         completeSquare=true;
               if(completeSquare==true)
                    System.out.println("Found a complete Square!");
                    displaySquare(sq);
          catch (Exception e)
               System.out.println("Error: " + e);
          System.exit(0);
     public static void displaySquare(char[][] square)
          for(int i=0; i<square.length; i++)
               for(int j=0; j<square.length; j++)
                    System.out.print(square[i][j]);
               System.out.println();
     public static int getRandom(int start, int end)//generates random int between 2 numbers
          Random rNum = new Random();
          int num = rNum.nextInt(end-start + 1) + start;
          return num;
     public static int bSearchPref(ArrayList list, String pref)
          int result = -1;
          int low = 0;
          int high = list.size()-1;
          String s="";
          while(low <= high && result==-1)
               int mid = (low + high)/2;
               s = (String)list.get(mid);
               if(s.startsWith(pref)==true)
                    result = mid;
               else if(pref.compareTo(list.get(mid))<0)
                    high = mid - 1;
               else
                    low = mid + 1;
          return result;
     public static int bSearchFull(ArrayList list, String word)
          int result = -1;
          int low = 0;
          int high = list.size()-1;
          while(low <= high && result==-1)
               int mid = (low + high)/2;
               if(word.compareTo(list.get(mid))==0)
                    result = mid;
               else if(word.compareTo(list.get(mid))<0)
                    high = mid - 1;
               else
                    low = mid + 1;
          return result;
     public static int getFirst(ArrayList list, String pref, int curr)
          int first=curr;
          boolean goodpref = true;
          while(goodpref==true && curr>=0)
               String s = (String)list.get(curr);
               if(s.startsWith(pref)==false)
                    goodpref=false;
                    curr++;
               else
                    curr--;
          if(curr<0)
               first=0;
          else
               first = curr;
          return first;
     public static int getLast(ArrayList list, String pref, int curr)
          int last=curr;
          boolean goodpref = true;
          while(goodpref==true)
               String s = (String)list.get(curr);
               if(s.startsWith(pref)==false)
                    goodpref=false;
                    curr--;
               else
                    curr++;
          if(curr<list.size())
               last = curr-1;
          else
               last = curr;
          return last;

Answer 1

It would help if you'd indicate exactly where these errors are ocurring. However...
sometimes i get
Error: java.lang.IllegalArgumentException: n must be
positive
So, whatever method you're calling there, you're passing a parameter that's zero or negative, when it must be positive.
and someteimes i get
Error: java.lang.ArrayIndexOutOfBoundsException: 2where the number 2 is always the size of the square
(strLength)It means you're trying to access an element at index 2 of an array that has at most two elements.
int[] arr = new int[2];
arr[0] = 0;
arr[1] = 1;
arr[2] =2 ; // OUT OF BOUNDS