public class Individual implements Comparable<Individual> {
private static long counter = 0;
private final long id = counter++;
private String name; // name is optional
public Individual(String name) { this.name = name; }
public Individual() {}
public String toString() {
return getClass().getSimpleName() + (name == null ? "" : " " + name);
}
public long id() { return id; }
public boolean equals(Object o) {
return o instanceof Individual && id == ((Individual)o).id;
}
public int hashCode() {
int result = 17;
if (name != null) {
result = 37 * result + name.hashCode();
}
result = 37 * result + (int) id;
return result;
}
public int compareTo(Individual arg) {
// Compare by class name first:
String first = getClass().getSimpleName();
String argFirst = arg.getClass().getSimpleName();
int firstCompare = first.compareTo(argFirst);
if (firstCompare != 0) {
return firstCompare;
}
if (name != null && arg.name != null) {
int secendCompare = name.compareTo(arg.name);
if (secendCompare != 0) {
return secendCompare;
}
}
return (arg.id < id ? -1 : (arg.id == id ? 0 : 1));
}
}
下面创建了一个抽象类PetCreator，以后我们通过调用arrayList()方法便可以直接获取相关Pet类的集合。这里使用到了我们上面没有提及的newInstance()方法，它会返回Class类所真正指代的类的实例，这是什么意思呢？比如说声明new Dog().getClass().newInstance()和直接new Dog()是等价的。
public abstract class PetCreator {
private Random rand = new Random(47);
// The List of the different getTypes of Pet to create:
public abstract List<Class<? extends Pet>> getTypes();
public Pet randomPet() {
// Create one random Pet
int n = rand.nextInt(getTypes().size());
try {
return getTypes().get(n).newInstance();
} catch (InstantiationException e) {
throw new RuntimeException(e);
} catch (IllegalAccessException e) {
throw new RuntimeException(e);
}
}
public Pet[] createArray(int size) {
Pet[] result = new Pet[size];
for (int i = 0; i < size; i++) {
result[i] = randomPet();
}
return result;
}
public ArrayList<Pet> arrayList(int size) {
ArrayList<Pet> result = new ArrayList<Pet>();
Collections.addAll(result, createArray(size));
return result;
}
}
接下来我们来实现上面这一个抽象类，解释一下下面的代码，在下面的代码中，我们声明了两个集合类，allTypes和types，其中allTypes中包含了我们呢上面所声明的所有类，但是我们具体的类型实际上只有两种即Mutt和EgypianMau，所以我们真正需要new出来的宠物只是types中所包含的类型，以后我们通过调用getTypes()便可以得到types中所包含的所哟类型。
public class LiteralPetCreator extends PetCreator {
@SuppressWarnings("unchecked")
public static final List<Class<? extends Pet>> allTypes = Collections.unmodifiableList(
Arrays.asList(Pet.class, Dog.class, Cat.class, Mutt.class, EgyptianMau.class));
private static final List<Class<? extends Pet>> types = allTypes.subList(
allTypes.indexOf(Mutt.class), allTypes.size());
public List<Class<? extends Pet>> getTypes() {
return types;
}
}
总体的逻辑已经完成了，最后我们实现用来统计集合中相关Pet类个数的TypeCounter类。解释一下isAssignalbeFrom()方法，它可以判断一个反射类是某个反射类的子类或者间接子类。而getSuperclass()顾名思义就是得到某个反射类的父类了。
public class TypeCounter extends HashMap<Class<?>, Integer> {
private Class<?> baseType;
public TypeCounter(Class<?> baseType) {
this.baseType = baseType;
}
public void count(Object obj) {
Class<?> type = obj.getClass();
if (!baseType.isAssignableFrom(type)) {
throw new RuntimeException(
obj + " incorrect type " + type + ", should be type or subtype of " + baseType);
}
countClass(type);
}
private void countClass(Class<?> type) {
Integer quantity = get(type);
put(type, quantity == null ? 1 : quantity + 1);
Class<?> superClass = type.getSuperclass();
if (superClass != null && baseType.isAssignableFrom(superClass)) {
countClass(superClass);
}
}
@Override
public String toString() {
StringBuilder result = new StringBuilder("{");
for (Map.Entry<Class<?>, Integer> pair : entrySet()) {
result.append(pair.getKey().getSimpleName());
result.append("=");
result.append(pair.getValue());
result.append(", ");
}
result.delete(result.length() - 2, result.length());
result.append("} ");
return result.toString();
}
}
