CSC 8310 -- Example Java program (Battleground)

Example Java program (Battleground)
Dr. David Matuszek, dave@acm.org, Villanova University

The idea of this program is that you have a Battleground containing some number of Fighters. Each Fighter fights only for himself. The program goes in a series of steps; at each step, each Fighter moves and, if he encounters another Fighter, fights to the death. The stronger Fighter always wins (if they are equally strong, the fighter who moved wins) and adds the strength from his vanquished opponent to his own strength. Play continues for a fixed number of steps or until there is only one Fighter left (whichever comes first).

class Fighter
{
  static int count;  // CLASS VARIABLE: how many fighters there are
  
  int strength = 1;      // my strength
  int direction;         // direction I'm facing
  Battleground place;    // the Battleground that I fight on
  int row, column;       // where I am
  int newRow, newColumn; // where I want to be
  int lastMoved = -1;    // last turn that I did something
  
  Fighter (Battleground place, int row, int column)  // Construct a Fighter.
  {
    direction = (int) (Math.random () * 4);  // face in a direction 0 to 3
    this.place = place;                      // remember my battleground
    this.row = row;                          // remember my location
    this.column = column;
    count++;                                 // count me
  }
  
  void doSomething (int step)
  {
    // If I've already moved, don't move again
    if (step == lastMoved) return;
    else lastMoved = step;

    // sometimes change direction (about 10% of the time)
    if (Math.random () < 0.10) direction = (int) (Math.random () * 4);
    
    // figure out where I want to be
    newRow = row; newColumn = column;
    switch (direction)
      {
      case 0: newRow = (row + 1) % place.size;                    break;
      case 1: newRow = (place.size + row - 1) % place.size;       break;
      case 2: newColumn = (column + 1) % place.size;              break;
      case 3: newColumn = (place.size + column - 1) % place.size; break;
      }
    
    // if that space is occupied, fight for it, else just move there
    if (place.warzone [newRow][newColumn] != null)
      fight (newRow, newColumn);
    else
      move (newRow, newColumn);
  }
  
  void move (int newRow, int newCol)      // Do a simple, uncontested move
  {
    place.warzone [row][column] = null;        // Move from here
    place.warzone [newRow][newColumn] = this;  // to here, and
    row = newRow; column = newColumn;          // remember where I am now.
  }
  
  void fight (int newRow, int newColumn) // Fight someone in that location
  {
    Fighter opponent = place.warzone [newRow][newColumn];

    if (strength >= opponent.strength)   // If I win,
      {
	strength += opponent.strength;   // take my opponent's strength
	move (newRow, newColumn);        // and position;
	Fighter.count--;                 // he's gone now, reduce count.
      }
    else
      {
	opponent.strength += strength;        // But if I lose,
	place.warzone [row][column] = null;   // erase myself
	Fighter.count--;                      // and count me gone.
      }
  }

  public String toString ()       // Represent a fighter by just his strength
  {
    if (strength < 10) return " " + strength;  // add a blank if < 10
    else return "" + strength;                 // else just convert to String
  }
}

public class Battleground
{
  int size;              // size of the battleground
  Fighter [][] warzone;  // array representing the battleground

  Battleground (int size)                   // Construct a Battleground.
  {
    warzone = new Fighter [size][size];     // Make the array
    this.size = size;                       // and remember how big it is.

    for (int i = 0; i < size; i++)          // Put a Fighter in 25% of
      for (int j = 0; j < size; j++)        // squares (the rest are initially
        if (Math.random () < 0.25)          // null).
	  warzone[i][j] = new Fighter (this, i, j);
  }
  
  void print ()                             // Print the Battleground.
  {
    for (int i = 0; i < size; i++)
      {
	for (int j = 0; j < size; j++)
	  {
	    if (warzone[i][j] == null) System.out.print (" --");
	    else System.out.print (" " + warzone[i][j]);
	  }
	System.out.println ();
      }
  }

  public static void main (String args[])
  {
    final int SIZE = 10;   // Constant: size of battleground
    final int STEPS = 10;  // Constant: number of steps to run simulation
    Battleground battleground = new Battleground (SIZE); // Make battleground.
    for (int step = 0; step < STEPS; step++)            // Run for STEPS steps.
      {
	System.out.println ("Step " + step + ", " +
			    Fighter.count + " fighters:");
	battleground.print ();

	if (Fighter.count == 1) break;     // Quit early if we have a winner,
	for (int i = 0; i < SIZE; i++)     // else loop through battleground
	  for (int j = 0; j < SIZE; j++)   // and let each Fighter doSomething.
	    if (battleground.warzone[i][j] instanceof Fighter)
	      battleground.warzone[i][j].doSomething (step);
      }
    System.out.println ("At end (" + Fighter.count + " fighters left):");
    battleground.print ();
  }
}

Code Outline

class Fighter
  Fighter (Battleground place, int row, int column)  // Construct a Fighter. 
  void doSomething (int step)
  void move (int newRow, int newCol)      // Do a simple, uncontested move
  void fight (int newRow, int newColumn) // Fight someone in that location
  public String toString ()       // Represent a fighter by just his strength

public class Battleground
  Battleground (int size)                   // Construct a Battleground.
  void print ()                             // Print the Battleground.
  public static void main (String args[])