Please help with my basic java implementation of Conway's game of life

Question

I have spent quite a while trying to write a program to implement Conway's game of life - Link with more info. . I am following some online guides and was given the majority of the functions. I wrote the "next" and "neighbours" methods shown below. Could anyone tell me if these are good implementations, and how they could be made better please ?

The point of the exercise was to not modify or change any of the other methods and just write the next method ! :)

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

public class Life {

private boolean[][] cells;

public static void main( String[] args ) {
  Life generation = new Life( );
  for (int i = 0; i != 10; i++) {
    System.out.println( generation );
    generation.next( );
  }
}
// Constructors

public void next (){

  int SIZE;
  SIZE=cells.length;
  boolean[][] tempCells = new boolean [SIZE] [SIZE]; 

  for( int i=0; i<SIZE; i++ ) {
 for( int j=0; j<SIZE; j++ ) {
  tempCells[i][j] = cells[i][j];
 }
  } 
  for (int row = 0; row < cells.length ; row++)
  {
    for (int col = 0 ; col < cells[row].length ; col++)
    {
      if ( neighbours(row, col) > 3  ||  neighbours(row, col) < 2 )
      {
        tempCells[row][col] = false;
      }
      else if (neighbours(row, col) == 3 )
      {
        tempCells[row][col] = true;
      }      

    }

  }
  cells = tempCells;

}


public int neighbours (int row, int col) {
  int acc=0;
  for ( int i = row -1; i <= row + 1 ; i++)
    {
     for (int j = col -1 ; j <= col + 1 ; j++)
       {
       try {
         if (cells[i][j]==true && (i != row || j!=col))
         {
           acc++;
         }          
       } catch ( ArrayIndexOutOfBoundsException f)
       {continue;}
     }
  }
  return acc;
}


// Initialises 6 * 6 grid with Glider pattern.
public Life( ) {
final int SIZE = 8;
// Arguably, this should have been a class (static) array.
final int[][] pairs = {{2,4},{3,3},{1,2},{2,2},{3,2}};
cells = new boolean[ SIZE ][ ];
for (int row = 0; row < SIZE; row ++) {
cells[ row ] = new boolean[ SIZE ];
}
for (int pair = 0; pair < pairs.length; pair ++) {
final int row = pairs[ pair ][ 0 ];
final int col = pairs[ pair ][ 1 ];
cells[ row ][ col ] = true;
}
}
 // Initialise size * size grid with random cells.
//public Life( int size ) {
//final Random rand = new Random( );
//cells = new boolean[ size ][ ];
//for (int row = 0; row < size; row ++) {
//cells[ row ] = new boolean[ size ];
//for (int col = 0; col < size; col ++) {
//cells[ row ][ col ] = (rand.nextInt( 2 ) == 0);
//}
//}
//}
// Public methods and helper methods.

@Override
public String toString( ) {
String result = "";
for (int row = 0; row < cells.length; row ++) {
final boolean[] column = cells[ row ];
for (int col = 0; col < column.length; col ++) {
result = result + (column[ col ] ? "x" : ".");
}
result = result + "\n";
}
return result;
}
}

Answer 1

You don't need to copy the contents of cells to tempCells (the first nested loop in next). Instead, you can add one extra clause to the if-else in the next loop. Also, storing the result from neighbours may be a good idea for both speed and clarity.

for (int row = 0; row < cells.length ; row++)
    for (int col = 0 ; col < cells[row].length ; col++) {
       int n = neighbours(row,col);

       if (n > 3  ||  n < 2)
           tempCells[row][col] = false;
       else if (n == 3)
           tempCells[row][col] = true;
       else
           tempCells[row][col] = cells[row][col];
    }

(Apart from that, looks fine, but I haven't run and tested your code.)

Answer 2

Don't use ArrayIndexOutOfBoundException to compute out-of-boundary (OOB) conditions. It kills performance. Better use the wrap-around mechanism to treat your array like a sphere so that you don't encounter OOBs at all. You could try something like this:

public Cell[] getNeighbours(int i, int j) {
int i2 = i - 1, i3 = i + 1, j2 = j - 1, j3 = j + 1;
if (i2 == -1) i2 = board.length - 1;
if (i3 == (board.length)) i3 = 0;
if (j2 == -1) j2 = board[i].length - 1;
if (j3 == (board[i].length)) j3 = 0;
return new Cell[]{board[i2][j2], board[i2][j], board[i2][j3], board[i][j2], board[i][j3], board[i3][j2], board[i3][j], board[i3][j3]};

}

Then you can loop through the returned array and check how many of those are alive and return that count.