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Semester 1/Programming 1/Java/examples/projects/chapter12/foxes-and-rabbits-v1/Rabbit.java

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+import java.util.List;
+import java.util.Random;
+
+/**
+ * A simple model of a rabbit.
+ * Rabbits age, move, breed, and die.
+ * 
+ * @author David J. Barnes and Michael Kölling
+ * @version 2016.02.29
+ */
+public class Rabbit
+{
+    // Characteristics shared by all rabbits (class variables).
+
+    // The age at which a rabbit can start to breed.
+    private static final int BREEDING_AGE = 5;
+    // The age to which a rabbit can live.
+    private static final int MAX_AGE = 40;
+    // The likelihood of a rabbit breeding.
+    private static final double BREEDING_PROBABILITY = 0.12;
+    // The maximum number of births.
+    private static final int MAX_LITTER_SIZE = 4;
+    // A shared random number generator to control breeding.
+    private static final Random rand = Randomizer.getRandom();
+    
+    // Individual characteristics (instance fields).
+    
+    // The rabbit's age.
+    private int age;
+    // Whether the rabbit is alive or not.
+    private boolean alive;
+    // The rabbit's position.
+    private Location location;
+    // The field occupied.
+    private Field field;
+
+    /**
+     * Create a new rabbit. A rabbit may be created with age
+     * zero (a new born) or with a random age.
+     * 
+     * @param randomAge If true, the rabbit will have a random age.
+     * @param field The field currently occupied.
+     * @param location The location within the field.
+     */
+    public Rabbit(boolean randomAge, Field field, Location location)
+    {
+        age = 0;
+        alive = true;
+        this.field = field;
+        setLocation(location);
+        if(randomAge) {
+            age = rand.nextInt(MAX_AGE);
+        }
+    }
+    
+    /**
+     * This is what the rabbit does most of the time - it runs 
+     * around. Sometimes it will breed or die of old age.
+     * @param newRabbits A list to return newly born rabbits.
+     */
+    public void run(List<Rabbit> newRabbits)
+    {
+        incrementAge();
+        if(alive) {
+            giveBirth(newRabbits);            
+            // Try to move into a free location.
+            Location newLocation = field.freeAdjacentLocation(location);
+            if(newLocation != null) {
+                setLocation(newLocation);
+            }
+            else {
+                // Overcrowding.
+                setDead();
+            }
+        }
+    }
+    
+    /**
+     * Check whether the rabbit is alive or not.
+     * @return true if the rabbit is still alive.
+     */
+    public boolean isAlive()
+    {
+        return alive;
+    }
+    
+    /**
+     * Indicate that the rabbit is no longer alive.
+     * It is removed from the field.
+     */
+    public void setDead()
+    {
+        alive = false;
+        if(location != null) {
+            field.clear(location);
+            location = null;
+            field = null;
+        }
+    }
+    
+    /**
+     * Return the rabbit's location.
+     * @return The rabbit's location.
+     */
+    public Location getLocation()
+    {
+        return location;
+    }
+    
+    /**
+     * Place the rabbit at the new location in the given field.
+     * @param newLocation The rabbit's new location.
+     */
+    private void setLocation(Location newLocation)
+    {
+        if(location != null) {
+            field.clear(location);
+        }
+        location = newLocation;
+        field.place(this, newLocation);
+    }
+
+    /**
+     * 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;
+    }
+
+    /**
+     * A rabbit can breed if it has reached the breeding age.
+     * @return true if the rabbit can breed, false otherwise.
+     */
+    private boolean canBreed()
+    {
+        return age >= BREEDING_AGE;
+    }
+}