Wireworld/Java

Works with: Java version 1.5+

With help from Conway's Game of Life#Java: <lang java5>public class Wireworld{

 public static final char empt = ' ';
 public static final char head = 'h';
 public static final char tail = 't';
 public static final char ctor = '.';

 public static char[][] iterate(char[][] world){
   char[][] nextGen = new char[world.length][world[0].length];
   for(int row = 0; row < world.length; row++){//each row
     String thisRow = new String(world[row]);
     for(int col = 0; col < thisRow.length(); col++){//each char in the row
       switch (world[row][col]) {
         case head:
           nextGen[row][col] = tail;
           continue;
         case tail:
           nextGen[row][col] = ctor;
           continue;
         case empt:
           nextGen[row][col] = empt;
           continue;
         default:
       }
       String above = "";//neighbors above
       String same = "";//neighbors in the same row
       String below = "";//neighbors below
       if(col == 0){//all the way on the left
         //no one above if on the top row
         //otherwise grab the neighbors from above
         above = (row == 0) ? null : new String(world[row - 1]).substring(col,
                 col + 2);
         same = thisRow.substring(col + 1, col + 2);
         //no one below if on the bottom row
         //otherwise grab the neighbors from below
         below = (row == world.length - 1) ? null : new String(world[row + 1]).substring(col, col + 2);
       }else if (col == thisRow.length() - 1){//right
         //no one above if on the top row
         //otherwise grab the neighbors from above
         above = (row == 0) ? null : new String(world[row - 1]).substring(col - 1,
                 col + 1);
         same = thisRow.substring(col - 1, col);
         //no one below if on the bottom row
         //otherwise grab the neighbors from below
         below = (row == world.length - 1) ? null : new String(world[row + 1]).substring(col - 1, col + 1);
       }else{//anywhere else
         //no one above if on the top row
         //otherwise grab the neighbors from above
         above = (row == 0) ? null : new String(world[row - 1]).substring(col - 1,
                 col + 2);
         same = thisRow.substring(col - 1, col) + thisRow.substring(col + 1, col + 2);
         //no one below if on the bottom row
         //otherwise grab the neighbors from below
         below = (row == world.length - 1) ? null : new String(world[row + 1]).substring(col - 1, col + 2);
       }
       int heads = headsInNeighborhood(above, same, below);
       switch (heads){
         case 1:
         case 2:
           nextGen[row][col] = head;
           break;
         default:
           nextGen[row][col] = ctor;
       }
     }
   }
   return nextGen;
 }

 private static int headsInNeighborhood(String above, String same, String below){
   int ans = 0;
   if(above != null){//no one above
     for(char x : above.toCharArray()){//each neighbor from above
       if(x == head){
         ans++;//count it if a head is here
       }
     }
   }
   for(char x : same.toCharArray()){//two on either side
     if(x == head){
       ans++;//count it if a head is here
     }
   }
   if(below != null){//no one below
     for(char x : below.toCharArray()){//each neighbor below
       if(x == head){
         ans++;//count it if a head is here
       }
     }
   }
   return ans;
 }

 public static void main(String[] args){
   char[][] world = {
     "th.........".toCharArray(),
     ".   .      ".toCharArray(),
     "   ...     ".toCharArray(),
     ".   .      ".toCharArray(),
     "ht.. ......".toCharArray()
   };
   for(int i = 0; i <= 20; i++){
     System.out.println("Iteration " + i + ":");
     printWorld(world);
     System.out.println();
     world = iterate(world);
   }
 }

 private static void printWorld(char[][] world){
   for(char[] row : world){
     System.out.println(row);
   }
 }

}</lang>

Output:

Iteration 0:
th.........
.   .      
   ...     
.   .      
ht.. ......

Iteration 1:
.th........
h   .      
   ...     
h   .      
t... ......

Iteration 2:
h.th.......
t   .      
   ...     
t   .      
.h.. ......

Iteration 3:
th.th......
.   h      
   ...     
.   .      
hth. ......

Iteration 4:
.th.th.....
h   t      
   hhh     
h   .      
t.th ......

Iteration 5:
h.th.th....
t   .      
   ttt     
t   .      
.h.t ......

Iteration 6:
th.th.th...
.   h      
   ...     
.   .      
hth. ......

Iteration 7:
.th.th.th..
h   t      
   hhh     
h   .      
t.th ......

Iteration 8:
h.th.th.th.
t   .      
   ttt     
t   .      
.h.t ......

Iteration 9:
th.th.th.th
.   h      
   ...     
.   .      
hth. ......

Iteration 10:
.th.th.th.t
h   t      
   hhh     
h   .      
t.th ......