Further abstraction techniques - Objects First with Java: A Practical Introduction Using BlueJ - page 333

Code 10.1
continued
The Rabbit class

/**
* Increase the age.
* This could result in the rabbit's death.
*/
private void incrementAge()
{

age++;
if (age > MAX_AGE) {
setDead();

}

}

/**
* Check whether or not this rabbit is to give birth at this step.
* New births will be made into free adjacent locations.
* @param newRabbits A list to return newly born rabbits.
*/
private void giveBirth(List<Rabbit> newRabbits)
{
// New rabbits are born into adjacent locations.
// Get a list of adjacent free locations.
List<Location> free = field.getFreeAdjacentLocations(location);
int births = breed();
for ( int b = 0; b < births && free.size() > 0; b++) {
Location loc = free.remove(0);
Rabbit young = new Rabbit(false, field, loc);
newRabbits.add(young);

}

}

/**
* Generate a number representing the number of births,
* if it can breed.
* @return The number of births (may be zero).
*/
private int breed()
{

int births = 0;
if (canBreed() && rand.nextDouble() <= BREEDING_PROBABILITY) {
births = rand.nextInt(MAX_LITTER_SIZE) + 1;

}
return births;

}

// other methods omitted

}