Logic of placeDotCom->Gamehelper

[Steve Issacs]

Hi, could someone explain the logic of the above method in GameHelper class on page 152 in a better way than these comments?:

public ArrayList<String> placeDotCom (int comSize) {
ArrayList<String> alphaCells = new ArrayList <String> ();
String [] alphacoords = new String [comSize]; // holds 'f6' type coords
String temp = null; // temporary String for concat
int [] coords = new int [comSize]; //current candidate coords
int attempts = 0; // current attempts counter
boolean success = false; //flag = found a good location?
int location = 0; //current starting location

comCount++; // nth dot com to place
int incr = 1; // set horizontal increment
if ((comCount % 2) == 1) { // if odd dot com (place vertically)
incr = gridLength; // set vertical increment
}

while ( ! success & attempts++ < 200) { // main search loop
location = (int) (Math.random () * gridSize) ; // get random starting point
//System.out.print (" try " + location);
int x = 0; //nth position in dotcom to place
success = true; //assume success
while (success && x < comSize) { // look for adjacent unused spots
if (grid [location] == 0) { // if not already used
coords[x++] = location; // save location
location += incr; // try 'next' adjacent
if (location >= gridSize) { // out of bounds - 'bottom'
success = false; // failure
}
if (x > 0 && (location % gridLength == 0)) { // out of bounds - right edge
success = false;
} // failure
} else {
// System.out.print (" used " + location ;
success = false; // failure
}
}
} // end while

int x = 0; // tour location into alpha coords
int row = 0;
int column = 0;
// System.out.println ("\n");
while ( x< comSize); {
grid[coords[x]] = 1; // mark master grid pts as 'used'
row = (int) (coords[x] / gridLength); // get row value
column = coords[x] % gridLength; // get numeric column value
temp = String.valueOf(alphabet.charAt(column)); //convert to alpha

alphaCells.add(temp.concat (Integer.toString(row))); //
x++;
// System.out.print (" coord "+x+ " = " alphaCells.get (x-1));
}
// System.out.println ("\n");

return alphaCells;
}
}

[Wouter Oet]

Please UseCodeTags and IsolateTheProblem. What don't you get?

[Janeice DelVecchio]

Welcome to javaranch.... I assume you're using the HeadFirst Java?

While I go dust mine off, you should try to edit your post and put all that code into code tags.... it'll make it easier to read

[Janeice DelVecchio]

At this point in the book, it's not really NECESSARY to understand each part of what's happening here, but we can break this down into pieces. Below is the method method call in code tags..... You'll note the method you pasted is one of the 2 methods in the GameHelper class. The other method handles user input.

The method is called in the DotComBust class, in the setUpGame() method:

 for (DotCom dotComSet : dotComsList) {
            ArrayList<String> newLocation = helper.placeDotCom(3);
            dotComSet.setLocationCells(newLocation);
        }   

Do you understand what's going on in this above code?

It's going to take me a little bit to mark up the other method for you....

[Janeice DelVecchio]

Here's your method marked up by me.

From here on in, if you don't understand something, copy and paste that part into a new post (using code tags) and we can go over it.

// method, placeDotCom, takes an int as a parameter, and returns an ArrayList of Strings
 public ArrayList<String> placeDotCom(int comSize) {                
    // declare ArrayList alphaCells
    ArrayList<String> alphaCells = new ArrayList<String>();
    // declare an array to hold the coordinates, size is equal to comSize
    String [] alphacoords = new String [comSize];      
    // declare a string to be used for concatenation
    String temp = null;                               
    // declare an array to hold candidate coordinates
    int [] coords = new int[comSize];                  
    // counter to keep track of how many attempts
    int attempts = 0;                                  
    // if success is true, that means it's a good place to hide the "dot com" 
    boolean success = false;                           
    int location = 0;                                  // current starting location
    
	// comcount is one of the member variables. It keeps track of how many dot coms are placed
    comCount++;                                        // nth dot com to place
	
	// this section says to place the dot com vertically if it's on an odd number
    int incr = 1;                                      // set horizontal increment
    if ((comCount % 2) == 1) {                         // if odd dot com  (place vertically)
      incr = gridLength;                               // set vertical increment
    }

	// this while loop figures out where in the array to place the dot com...
	// ... it keeps going until success == true, or until it searches 200 times
    while ( !success & attempts++ < 200 ) {             // main search loop  (32)
	location = (int) (Math.random() * gridSize);      // get random starting point
        //System.out.print(" try " + location);
	int x = 0;                                        // nth position in dotcom to place
        success = true;                                 // assume success
        while (success && x < comSize) {                // look for adjacent unused spots
          if (grid[location] == 0) {                    // if not already used
             coords[x++] = location;                    // save location
             location += incr;                          // try 'next' adjacent
             if (location >= gridSize){                 // out of bounds - 'bottom'
               success = false;                         // failure
             }
             if (x>0 & (location % gridLength == 0)) {  // out of bounds - right edge
               success = false;                         // failure
             }
          } else {                                      // found already used location
              // System.out.print(" used " + location);  
              success = false;                          // failure
          }
        }
    }                                                   // end while

	// this section takes the successful find and turns it into coordinates for the game
    int x = 0;                                          // turn good location into alpha coords
    int row = 0;
    int column = 0;
    // System.out.println("\n");
    while (x < comSize) {
      grid[coords[x]] = 1;                              // mark master grid pts. as 'used'
      row = (int) (coords[x] / gridLength);             // get row value
      column = coords[x] % gridLength;                  // get numeric column value
      temp = String.valueOf(alphabet.charAt(column));   // convert to alpha
      
	  // add the coordinate to the arraylist
      alphaCells.add(temp.concat(Integer.toString(row)));
      x++;

      // System.out.print("  coord "+x+" = " + alphaCells.get(x-1));
      
    }
    // System.out.println("\n");
    
    return alphaCells; // send the arraylist back to be used by the game
   }    

[Steve Issacs]

Thanks! yes, i understand the invocation of this method.