AOOB exception in my CODE-PLEASE HELP!

[Danielle Honigman]

Hi There!
I am a newbie to java (and programming in general) and have been working on programming a simple text-based version of Conway's Game of Life. Everything was working perfectly when I had a fixed 10 by 10 array, but then I decided it would be more interesting to have static variables x and y for the length and width of the array so that you could easily change the dimensions of the playing board. So, I did that, and when I initialized them to any value (>= 10 since my start patterns were made with a 10 by 10 in mind) the program worked fine and printed boards of the indicated size. HOWEVER, when I extended that a bit and added some code prompting the user to indicate the desired dimensions, the program compiled correctly but then when it was running I got an ArrayIndexOutOfBoundsException and I can't seem to fix it. I know the error most
likely lies somewhere in the user-prompting code, but everything seems fine to me. I think for some reason the JVM is reading whatever number
I type in first (which is when you're prompted to choose a start pattern between 1 and 7) as the dimensions, but I'm not sure why. I have been tearing my hair out trying to debug this program, so I would GREATLY appreciate any help anyone could provide!
My code would probably be helpful =-P so here it is...I hope it's readable after all this cutting and pasting into this forum:

public class GameOfLife2 {
    
    //static int userWidth;
    //static int userHeight;
    static int x;   // static variable corresponding to the width of 
                    // the board (later specified by the user)
    static int y;   // static variable corresponding to the heigth of 
                    // the board (later specified by the user)
 
    static int[][] CurrentGen = new int[x][y];
    static int[][] NextGen = new int[x][y];
 
    public static void main(String[] args) {
        
        BufferedReader reader = new BufferedReader(new
                InputStreamReader(System.in));
        boolean gotValidNumGen = false;
        int numGen = 0;
        boolean gotValidNumber = false;
        int inputNumber = 0;
        int secPause = 0;
        boolean gotValidPause = false;
        //int x;
        //int y;
        boolean gotValidWidth = false;
        boolean gotValidHeight = false;
        
        // initializing elements of CurrentGen[][] to 0
        for (int i = 0; i < x; i++) {
            for (int j = 0; j < y; j++) {
                CurrentGen[i][j] = 0; 
            }
        }
    
        // prompting user for a start pattern (with exception-handling):
    
        do {
 
            System.out.println("\nPlease choose a starting pattern by typing the " + 
                               "integer corresponding to the choice you would like.");
            System.out.println();
            System.out.println("(1) Cross ");
            System.out.println("(2) Oscillator ");
            System.out.println("(3) Glider ");
            System.out.println("(4) R-pentamino ");
            System.out.println("(5) Exploder ");
            System.out.println("(6) Still Life ");
            System.out.println("(7) Randomly generated pattern");
        
            try {
                inputNumber = Integer.parseInt(reader.readLine());
                gotValidNumber = true;
            } catch (NumberFormatException nfe) {
                System.out.println("That is not a valid integer. Please try again.");
            } catch (IOException ioe) {
                System.out.println("I/O Exception occurred");   
            }
        }
 
        while (!gotValidNumber);
 
        switch (inputNumber) {
 
        case 1:             // setting cross pattern
 
            for (int j = 0; j < 10; j++) 
                CurrentGen[4][j] = 1;
 
            for (int i = 0; i < 10; i++)
                CurrentGen[i][4] = 1;
 
            break; 
 
        case 2:             // setting oscillator pattern
 
            for (int j = 4; j <= 6; j++) 
                CurrentGen[3][j] = 1;
 
            for (int j = 3; j <= 5; j++)
                CurrentGen[4][j] = 1;
 
            break;
 
        case 3:         // setting glider pattern
 
            CurrentGen[2][1] = 1;
            CurrentGen[2][3] = 1;
            CurrentGen[3][2] = 1;
            CurrentGen[3][3] = 1;
            CurrentGen[1][3] = 1;
 
            break;
 
        case 4:         // setting R-pentamino pattern
 
            CurrentGen[3][4] = 1;
            CurrentGen[3][5] = 1;
            CurrentGen[4][3] = 1;
            CurrentGen[4][4] = 1;
            CurrentGen[5][4] = 1;
 
            break;
 
        case 5:             // setting exploder pattern
 
            CurrentGen[3][5] = 1;
            CurrentGen[4][4] = 1;
            CurrentGen[4][5] = 1;
            CurrentGen[4][6] = 1;
            CurrentGen[5][4] = 1;
            CurrentGen[5][6] = 1;
            CurrentGen[6][5] = 1;
 
            break;
 
        case 6:         // setting still-life pattern
 
            CurrentGen[2][4] = 1;
            CurrentGen[2][5] = 1;
            CurrentGen[3][3] = 1;
            CurrentGen[3][5] = 1;
            CurrentGen[4][3] = 1;
            CurrentGen[4][4] = 1;
 
            break;
 
        case 7:     // setting random pattern
 
            for (int i = 0; i < x; i++) {
                for (int j = 0; j < y; j++) {
                    CurrentGen[i][j] = (int) (Math.random() * 2);
                } 
            }
        }
 
        for (int s = 0; s <= 0; s++) {
            // prompting user for the desired board size (with exception-handling):
    
            do {
 
                System.out.println();
                System.out.println("What dimensions would you like the board to have?");
                System.out.println();
                System.out.println("When prompted, please type an integer corresponding " + 
                                   "to the desired width and height of the board.");
                System.out.println("The MINIMUM possible dimensions are 10 by 10.");
                System.out.println();
                System.out.print("What is the width you would like? ");
                try {
                    x = Integer.parseInt(reader.readLine());
                    gotValidWidth = true;
                } catch (NumberFormatException nfe) {
                    gotValidWidth = false;
                    System.out.println("That is not a valid integer. Please try again.");
                } catch (IOException ioe) {}
 
            }            
            while (!gotValidWidth);
        }
        //if (x < 10) {
        //System.out.println("Sorry, but that is not a valid width. 
        //(The minimum possible width is 10). The default width of 10 will be used.");
        //x = 10;
        //}
        for (int s = 0; s <= 0; s++) {
            do {
                System.out.println();
                System.out.print("What is the height you would like? ");
 
                try {
                    y = Integer.parseInt(reader.readLine());
                    gotValidHeight = true;
 
                } catch (NumberFormatException nfe) {
                    gotValidHeight = false;
                    System.out.println("That is not a valid integer. Please try again.");
                } catch (IOException ioe) {}
            }
 
            while (!gotValidHeight);
    
            //if (y < 10) {
 
            //System.out.println("Sorry, but that is not a valid height. 
            //(The minimum possible height is 10). The default height of 10 will be used.");
            //y = 10; 
            //}
        }     
        // prompting user for the desired number of generations 
        // to be generated (with exception-handling):
    
        do {
 
            System.out.println();
            System.out.print("How many generations would you like to be generated? " + 
                             "(please type an integer corresponding to that number): ");
 
            try {
 
                numGen = Integer.parseInt(reader.readLine());
                gotValidNumGen = true;
            } catch (NumberFormatException nfe) {
                System.out.println("That is not a valid integer. Please try again.");
                gotValidNumGen = false;
            } catch (IOException ioe) {}
        }
 
        while (!gotValidNumGen);
    
        // prompting user for the desired pause between generations (with exception-handling):
 
        do {
 
            System.out.println();
            System.out.print("How much of a pause would you like between generations? " + 
                             "(please type an integer corresponding to the # of seconds) ");
 
            try {
 
                secPause = Integer.parseInt(reader.readLine());
                gotValidPause = true;
            } catch (NumberFormatException nfe) {
                System.out.println("That is not a valid integer. Please try again.");
            } catch (IOException ioe) {}
        }
 
        while (!gotValidPause);
 
        // printing start pattern:
        System.out.println("\nInitial generation: "); 
        System.out.println();
        for (int i = 0; i < CurrentGen.length; i++) {
            for (int j = 0; j < CurrentGen[i].length; j++) 
                if (CurrentGen[i][j] == 1)
                    System.out.print("* ");
                else 
                    System.out.print("- ");
 
            System.out.println();
        }
        
        // having the Game iterate however many times the user specified
        for (int z = 1; z <= numGen; z++) {
 
            NextGeneration(); // call to method which determines the next generation
            
            //pausing the amount specified by the user (before next generation is printed)
            for (int p = 0; p <= (100000000 * secPause); p++) {}
 
            System.out.println();
            System.out.println("Here comes generation " + z + "...");
            System.out.println();
            // printing next generation
            for (int i = 0; i < CurrentGen.length; i++) {
                for (int j = 0; j < CurrentGen[i].length; j++) 
                    if (CurrentGen[i][j] == 1)
                        System.out.print("* ");
                    else 
                        System.out.print("- ");
                System.out.println();
            }                                  
        }
    }
 
    /************Method to determine number of neighbors of a given
     cell***************/
 
    public static int numOfNeighbors(int r, int c) {
        
        int numNeighbors = 0;       // initializing  the number of neighbors to 0
 
        if ((r - 1) >= 0 && (c - 1) >= 0 && (r - 1) < x && (c - 1) < y &&
            CurrentGen[r - 1][c - 1] == 1) {
            numNeighbors++;
        }
 
        if ((r - 1) >= 0 && c >= 0 && (r - 1) < x && c < y && CurrentGen[r - 1][c] == 1) {
            numNeighbors++;
        }
 
        if ((r - 1) >= 0 && (c + 1) >= 0 && (r - 1) < x && (c + 1) < y &&
            CurrentGen[r - 1][c + 1] == 1) {
            numNeighbors++;
        }
 
        if (r >= 0 && (c - 1) >= 0 && r < x && (c - 1) < y && CurrentGen[r][c - 1] == 1) {
            numNeighbors++;
        }
 
        if (r >= 0 && (c + 1) >= 0 && r < x && (c + 1) < y && CurrentGen[r][c + 1] == 1) {
            numNeighbors++;
        }
 
        if ((r + 1) >= 0 && (c - 1) >= 0 && (r + 1) < x && (c - 1) < y &&
            CurrentGen[r + 1][c - 1] == 1) {
            numNeighbors++;
        }
 
        if ((r + 1) >= 0 && c >= 0 && (r + 1) < x && c < y && CurrentGen[r + 1][c] == 1) {
            numNeighbors++;
        }
 
        if ((r + 1) >= 0 && (c + 1) >= 0 && (r + 1) < x && (c + 1) < y &&
            CurrentGen[r + 1][c + 1] == 1) {
            numNeighbors++;
        }
 
        return numNeighbors;
    }
 
    /***going through a generation and applying the rules to determine the
     next generation***/
 
    public static void NextGeneration() {
 
        for (int r = 0; r < x; r++) {
            for (int c = 0; c < y; c++) {                                                    
                int numOfNeighbors = numOfNeighbors(r, c); // getting the number of neighbors
                
                /***Conway's rules***/
    
                switch (numOfNeighbors) {
                    case 2:  
                        NextGen[r][c] = CurrentGen[r][c];   // a cell, whether occupied or empty,
                        break;                              // will stay the same if it has 2 neighbors
                        
                    case 3:
                        NextGen[r][c] = 1;  // an occupied cell with 3 neighbors will stay occupied
                        break;              // an empty cell with 3 neighbors will become occupied
                        
                    default:  
                        NextGen[r][c] = 0;     // otherwise, a cell stays empty or becomes empty 
                    }                          // (b/c it had more than 3 or less than 2 neighbors)
            }
        }
        
        /**when finished checking, copy NextGen to CurrentGen**/
        for (int i = 0; i < x; i++) {
            for (int j = 0; j < y; j++)
                CurrentGen[i][j] = NextGen[i][j];
        }
    }
} 

Thanks in advance for your help!
[ June 04, 2002: Message edited by: Dirk Schreckmann ]

[Manfred Leonhardt]

Hi Danielle,
I would make some small changes in the way your program is laid out. I would start with creating a method to get the valid integer. It will make your code look much cleaner:

  private static int getValidInteger( BufferedReader rd, String query, 
                                      int lower, int upper )
  {
    boolean validNumber = false;
    int inNumber = 0;
    do
    {
      System.out.println( query );
      try
      {
        inNumber = Integer.parseInt( rd.readLine() );
        if( inNumber < lower || inNumber > upper )
        {
          throw new NumberFormatException();
        }
        validNumber = true;
      }
      catch( NumberFormatException nfe )
      {
        System.out.println("That is not a valid integer. Please try again.");
      }
      catch( IOException ioe )
      {
        System.out.println("I/O Exception occurred");
      }
    } while( !validNumber );
    return( inNumber );
  }

The using that routine, you can request some information from the user. One big change to your program will have to be the use of initialization when declaring the variables. This must stop because once an array in Java is initialized its' size is fixed from then on. Also Java initializes all arrays with zero values so you don't need to do that explicitly.
Another few changes:
1. Ask user for size of board first so we can initialize the array before we are going to use it.
2. Don't use for loop to pause for a certain amount of time. Loops are dependent on processor speed and don't care about time clocks. Use the sleep method of Thread which takes a parameter of milliseconds to sleep for.
Now the modified main method:

  public static void main( String[] args )
  {
    BufferedReader reader = new BufferedReader( new InputStreamReader( System.in ) );
    //
    // Prompt user for width and height.
    //
    System.out.println("\nWhen prompted, please type an integer corresponding " +
                        "to the desired width and height of the board.");
    System.out.println("The MINIMUM possible dimensions are 10 by 10.\n");
    String query = "What is the width you would like?";
    x = getValidInteger( reader, query, 10, Integer.MAX_VALUE );
    query = "What is the height you would like?";
    y = getValidInteger( reader, query, 10, Integer.MAX_VALUE );
    CurrentGen = new int[x][y];
    NextGen = new int[x][y];
    //
    // prompting user for a start pattern (with exception-handling):
    //
    StringBuffer sb = new StringBuffer( "\nPlease choose a starting pattern " +
                                        "by typing the integer corresponding " +
                                        "to the choice you would like.\n");
    sb.append( "(1) Cross \n" );
    sb.append( "(2) Oscillator\n" );
    sb.append( "(3) Glider\n" );
    sb.append( "(4) R-pentamino\n" );
    sb.append( "(5) Exploder\n" );
    sb.append( "(6) Still Life\n" );
    sb.append( "(7) Randomly generated pattern\n" );
    query  = sb.toString() + "\nWhich pattern would you like?";
    int patternType = getValidInteger( reader, query, 1, 7 );
    switch( patternType )
    {
      case 1:
        // setting cross pattern
        for (int j = 0; j < 10; j++)
          CurrentGen[4][j] = 1;
        for (int i = 0; i < 10; i++)
          CurrentGen[i][4] = 1;
        break;
      case 2:
        // setting oscillator pattern
        for (int j = 4; j <= 6; j++)
          CurrentGen[3][j] = 1;
        for (int j = 3; j <= 5; j++)
          CurrentGen[4][j] = 1;
        break;
      case 3:
        // setting glider pattern
        CurrentGen[2][1] = 1;
        CurrentGen[2][3] = 1;
        CurrentGen[3][2] = 1;
        CurrentGen[3][3] = 1;
        CurrentGen[1][3] = 1;
        break;
      case 4:
        // setting R-pentamino pattern
        CurrentGen[3][4] = 1;
        CurrentGen[3][5] = 1;
        CurrentGen[4][3] = 1;
        CurrentGen[4][4] = 1;
        CurrentGen[5][4] = 1;
        break;
      case 5:
        // setting exploder pattern
        CurrentGen[3][5] = 1;
        CurrentGen[4][4] = 1;
        CurrentGen[4][5] = 1;
        CurrentGen[4][6] = 1;
        CurrentGen[5][4] = 1;
        CurrentGen[5][6] = 1;
        CurrentGen[6][5] = 1;
        break;
      case 6:
        // setting still-life pattern
        CurrentGen[2][4] = 1;
        CurrentGen[2][5] = 1;
        CurrentGen[3][3] = 1;
        CurrentGen[3][5] = 1;
        CurrentGen[4][3] = 1;
        CurrentGen[4][4] = 1;
        break;
      case 7:
        // setting random pattern
        for (int i = 0; i < x; i++)
        {
          for (int j = 0; j < y; j++)
          {
            CurrentGen[i][j] = (int) (Math.random() * 2);
          }
        }
    }
    //
    // prompting user for the desired number of generations
    // to be generated (with exception-handling):
    //
    query = "How many generations would you like to be generated?";
    int numGen = getValidInteger( reader, query, 0, Integer.MAX_VALUE );
    //
    // prompting user for the desired pause between generations 
    //
    query = "How many seconds should be between generations?";
    int secPause = getValidInteger( reader, query, 0, Integer.MAX_VALUE );
    //
    // printing start pattern:
    //
    System.out.println("\nInitial generation:\n");
    for (int i = 0; i < CurrentGen.length; i++)
    {
      for( int j = 0; j < CurrentGen[i].length; j++ )
      {
        if (CurrentGen[i][j] == 1)
        {
          System.out.print("* ");
        }
        else
        {
          System.out.print("- ");
        }
      }
      System.out.println();
    }
    // having the Game iterate however many times the user specified
    for( int z = 1; z <= numGen; z++ )
    {
      NextGeneration(); // call to method which determines the next generation
      //
      //pausing the amount specified by the user (before next generation is printed)
      //
      try
      {
        Thread.sleep( secPause*1000 );
      }
      catch( InterruptedException ie ) 
      {}
      System.out.println();
      System.out.println("Here comes generation " + z + "...");
      System.out.println();
      // printing next generation
      for (int i = 0; i < CurrentGen.length; i++)
      {
        for (int j = 0; j < CurrentGen[i].length; j++)
          if (CurrentGen[i][j] == 1)
            System.out.print("* ");
          else
            System.out.print("- ");
          System.out.println();
      }
    }
  }

Enjoy,
Manfred.

[Jessica Sant]

The problem is your array CurrentGen is never being initialized... so when the numOfNeighbors() method is executed and tries to access one of the elements in the uninitialized array -- it throws an ArrayIndexOutOfBounds Exception.

public class GameOfLife2 {
    static int x;   //Default initialization = 0
    static int y;   //Default initialization = 0
    static int[][] CurrentGen = new int[x][y];
    static int[][] NextGen = new int[x][y];
    public static void main(String[] args) {
      
        // This is never executed because both x and y == 0
        for (int i = 0; i < x; i++) {
            for (int j = 0; j < y; j++) {
                CurrentGen[i][j] = 0;
            }
        }

So you need to move the initialization of your CurrentGen[] array to AFTER you've assigned values to x and y.

[Manfred Leonhardt]

Hi Jessica,
If it were only that simple. As I have stated in my post:
Array size is immutable
What does that mean? Well it means that if I have a static variable (gets declared and initialized at class loading time):
static int[][] array = new int[0][0];
I can never change the size of array.
Therefore, the only solution is to stop doing the initialization in the declaration part and do it inside the constructor after the correct sizes are specified.
Regards,
Manfred.

[Jessica Sant]

.... caught me ...

[Danielle Honigman]

Hi Manfred,
First off, thanks so much for taking all the time and effort to right such a helpful reply! I really like your suggestion of creating a method to get a valid integer from the user, because that makes things a lot easier since everything I'm getting from the user happens to be integers (since that's all I really know the java syntax for as of now). Just a question about that..is there any reason why you create a string buffer object (constructor method?--sorry I am still very new to object-oriented concepts) to display the pattern options on the screen? Oh..good point about the pausing..I didn't even think about the fact that a for loop depends on procesing speed..I was sure there had to be a pause method but I was just using that for the time beign..thanks so much for the info! okay last but def most important: when i modified my code with your corrections i ran into the problem that CurrentGen[][] and NextGen[][] were not being recognized in my NextGeneration() and NumNeighbors() methods...how exactly do I fix that? I tried making C.G[][] and N.G[][] static int arrays rather than just int arrays like you had, but of course that gave me an "invalid start" error because u can only declare static variables at the beginning of the class, so I'm not sure how to resolve that . If you have any ideas I would truly appreciate it. Thanks again!!!

[Manfred Leonhardt]

HI Danielle,
Here is the complete code that works for me without any errors. Take a look at it and compare with what you have.

import java.io.*;
import java.util.*;
public class GameOfLife2
{
  private static int x;
  private static int y;
  private static int[][] CurrentGen;
  private static int[][] NextGen;
  private static int getValidInteger( BufferedReader rd, String query, 
                                      int lower, int upper )
  {
    boolean validNumber = false;
    int inNumber = 0;
    do
    {
      System.out.println( query );
      try
      {
        inNumber = Integer.parseInt( rd.readLine() );
        if( inNumber < lower || inNumber > upper )
        {
          throw new NumberFormatException();
        }
        validNumber = true;
      }
      catch( NumberFormatException nfe )
      {
        System.out.println("That is not a valid integer. Please try again.");
      }
      catch( IOException ioe )
      {
        System.out.println("I/O Exception occurred");
      }
    } while( !validNumber );
    return( inNumber );
  }
  public static void main( String[] args )
  {
    BufferedReader reader = new BufferedReader( new InputStreamReader( System.in ) );
    //
    // Prompt user for width and height.
    //
    System.out.println("\nWhen prompted, please type an integer corresponding " +
                        "to the desired width and height of the board.");
    System.out.println("The MINIMUM possible dimensions are 10 by 10.\n");
    String query = "What is the width you would like?";
    x = getValidInteger( reader, query, 10, Integer.MAX_VALUE );
    query = "What is the height you would like?";
    y = getValidInteger( reader, query, 10, Integer.MAX_VALUE );
    CurrentGen = new int[x][y];
    NextGen = new int[x][y];
    //
    // prompting user for a start pattern (with exception-handling):
    //
    StringBuffer sb = new StringBuffer( "\nPlease choose a starting pattern " +
                                        "by typing the integer corresponding " +
                                        "to the choice you would like.\n");
    sb.append( "(1) Cross \n" );
    sb.append( "(2) Oscillator\n" );
    sb.append( "(3) Glider\n" );
    sb.append( "(4) R-pentamino\n" );
    sb.append( "(5) Exploder\n" );
    sb.append( "(6) Still Life\n" );
    sb.append( "(7) Randomly generated pattern\n" );
    query  = sb.toString() + "\nWhich pattern would you like?";
    int patternType = getValidInteger( reader, query, 1, 7 );
    switch( patternType )
    {
      case 1:
        // setting cross pattern
        for (int j = 0; j < 10; j++)
          CurrentGen[4][j] = 1;
        for (int i = 0; i < 10; i++)
          CurrentGen[i][4] = 1;
        break;
      case 2:
        // setting oscillator pattern
        for (int j = 4; j <= 6; j++)
          CurrentGen[3][j] = 1;
        for (int j = 3; j <= 5; j++)
          CurrentGen[4][j] = 1;
        break;
      case 3:
        // setting glider pattern
        CurrentGen[2][1] = 1;
        CurrentGen[2][3] = 1;
        CurrentGen[3][2] = 1;
        CurrentGen[3][3] = 1;
        CurrentGen[1][3] = 1;
        break;
      case 4:
        // setting R-pentamino pattern
        CurrentGen[3][4] = 1;
        CurrentGen[3][5] = 1;
        CurrentGen[4][3] = 1;
        CurrentGen[4][4] = 1;
        CurrentGen[5][4] = 1;
        break;
      case 5:
        // setting exploder pattern
        CurrentGen[3][5] = 1;
        CurrentGen[4][4] = 1;
        CurrentGen[4][5] = 1;
        CurrentGen[4][6] = 1;
        CurrentGen[5][4] = 1;
        CurrentGen[5][6] = 1;
        CurrentGen[6][5] = 1;
        break;
      case 6:
        // setting still-life pattern
        CurrentGen[2][4] = 1;
        CurrentGen[2][5] = 1;
        CurrentGen[3][3] = 1;
        CurrentGen[3][5] = 1;
        CurrentGen[4][3] = 1;
        CurrentGen[4][4] = 1;
        break;
      case 7:
        // setting random pattern
        for (int i = 0; i < x; i++)
        {
          for (int j = 0; j < y; j++)
          {
            CurrentGen[i][j] = (int) (Math.random() * 2);
          }
        }
    }
    //
    // prompting user for the desired number of generations
    // to be generated (with exception-handling):
    //
    query = "How many generations would you like to be generated?";
    int numGen = getValidInteger( reader, query, 0, Integer.MAX_VALUE );
    //
    // prompting user for the desired pause between generations 
    //
    query = "How many seconds should be between generations?";
    int secPause = getValidInteger( reader, query, 0, Integer.MAX_VALUE );
    //
    // printing start pattern:
    //
    System.out.println("\nInitial generation:\n");
    for (int i = 0; i < CurrentGen.length; i++)
    {
      for( int j = 0; j < CurrentGen[i].length; j++ )
      {
        if (CurrentGen[i][j] == 1)
        {
          System.out.print("* ");
        }
        else
        {
          System.out.print("- ");
        }
      }
      System.out.println();
    }
    // having the Game iterate however many times the user specified
    for( int z = 1; z <= numGen; z++ )
    {
      NextGeneration(); // call to method which determines the next generation
      //
      //pausing the amount specified by the user (before next generation is printed)
      //
      try
      {
        Thread.sleep( secPause*1000 );
      }
      catch( InterruptedException ie ) 
      {}
      System.out.println();
      System.out.println("Here comes generation " + z + "...");
      System.out.println();
      // printing next generation
      for (int i = 0; i < CurrentGen.length; i++)
      {
        for (int j = 0; j < CurrentGen[i].length; j++)
          if (CurrentGen[i][j] == 1)
            System.out.print("* ");
          else
            System.out.print("- ");
          System.out.println();
      }
    }
  }
  /************Method to determine number of neighbors of a given     cell***************/
  public static int numOfNeighbors(int r, int c)
  {
    int numNeighbors = 0;
    // initializing  the number of neighbors to 0
    if ((r - 1) >= 0 && (c - 1) >= 0 && (r - 1) < x && (c - 1) < y &&
        CurrentGen[r - 1][c - 1] == 1)
    {
      numNeighbors++;
    }
    if ((r - 1) >= 0 && c >= 0 && (r - 1) < x && c < y && CurrentGen[r - 1][c] == 1)
    {
      numNeighbors++;
    }
    if ((r - 1) >= 0 && (c + 1) >= 0 && (r - 1) < x && (c + 1) < y &&
        CurrentGen[r - 1][c + 1] == 1)
    {
      numNeighbors++;
    }
    if (r >= 0 && (c - 1) >= 0 && r < x && (c - 1) < y && CurrentGen[r][c - 1] == 1)
    {
      numNeighbors++;
    }
    if (r >= 0 && (c + 1) >= 0 && r < x && (c + 1) < y && CurrentGen[r][c + 1] == 1)
    {
      numNeighbors++;
    }
    if ((r + 1) >= 0 && (c - 1) >= 0 && (r + 1) < x && (c - 1) < y &&
         CurrentGen[r + 1][c - 1] == 1)
    {
      numNeighbors++;
    }
    if ((r + 1) >= 0 && c >= 0 && (r + 1) < x && c < y && CurrentGen[r + 1][c] == 1)
    {
      numNeighbors++;
    }
    if ((r + 1) >= 0 && (c + 1) >= 0 && (r + 1) < x && (c + 1) < y &&
         CurrentGen[r + 1][c + 1] == 1)
    {
      numNeighbors++;
    }
    return numNeighbors;
  }
  /***going through a generation and applying the rules to determine the
  next generation***/
  public static void NextGeneration()
  {
    for (int r = 0; r < x; r++)
    {
      for (int c = 0; c < y; c++)
      {
        int numOfNeighbors = numOfNeighbors(r, c);
        // getting the number of neighbors
        /***Conway's rules***/
        switch (numOfNeighbors)
        {
          case 2:
            NextGen[r][c] = CurrentGen[r][c];
            // a cell, whether occupied or empty,
            break;
          // will stay the same if it has 2 neighbors
          case 3:
            NextGen[r][c] = 1;
            // an occupied cell with 3 neighbors will stay occupied
            break;
          // an empty cell with 3 neighbors will become occupied
          default:
            NextGen[r][c] = 0;
            // otherwise, a cell stays empty or becomes empty
        }
        // (b/c it had more than 3 or less than 2 neighbors)
      }
    }
    /**when finished checking, copy NextGen to CurrentGen**/
    for (int i = 0; i < x; i++)
    {
      for (int j = 0; j < y; j++)
        CurrentGen[i][j] = NextGen[i][j];
    }
  }
}

Regards,
Manfred.

[Danielle Honigman]

ah, very stupid mistake...I forgot to declare the static arrays in the beggining of the class and just did the declaration and initiation in the method, which explains why the other methods weren't recognizing the arrays (since they weren't static). Thanks!!! =)