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.)