Contents

1. 1. Animal.java:
2. 2. Dog.java:
3. 3. Cat.java:
4. 4. Generator.java:

Animal.java:

package lianxi;

public class Animal {
	String name;
	
	public Animal(){ }
	
	
	public Animal(String name){
		setName(name);
	}
	
	public String getName(){
		return name;
	}
	
	public void setName(String name){
		this.name = name;
	}
	
	public String toString(){
		return "My name is " + name;
	}
}

Dog.java:

package lianxi;

public class Dog extends Animal{
	private static long count = 0;
	
	private final long id = count++;
	
	public Dog(){
		super("default");
	}
	
	public Dog(String name){
		super(name);
	}
	
	@Override
	public String getName(){
		return super.getName();
	}
	
	@Override
	public void setName(String name){
		super.setName(name);
	}
	
	public String toString(){
		return getClass().getSimpleName() + " " + super.name + " " + id;
	}
}

Cat.java:

package lianxi;

public class Cat extends Animal{
	private static long count = 0;
	
	private final long id = count++;
	
	public Cat(){
		super("default");
	}
	
	public Cat(String name){
		super(name);
	}
	
	@Override
	public String getName(){
		return super.getName();
	}
	
	@Override
	public void setName(String name){
		super.setName(name);
	}
	
	@Override
	public String toString(){
		return getClass().getSimpleName() + " " + super.name + " " + id;
	}
}

Generator.java:

package lianxi;

public interface Generator<T> {
	T RandomNext();
}

AnimalGenerator.java:
package lianxi;

import java.util.Iterator;
import java.util.Random;

//支持foreach迭代循环的学生集合类要继承Iterable接口 
public class AnimalGenerator implements Generator<Animal>, Iterable<Animal>{
	//存储动物的种类
	private Class[] types = {Dog.class, Cat.class};
	
	private static Random rand = new Random(47);
	
	public AnimalGenerator() {}
	
	//For Generator Interface
	@Override
	public Animal RandomNext() {
		try{//返回一个随机动物种类的实例
			return (Animal)types[rand.nextInt(types.length)].newInstance();
		}catch(Exception e){
			throw new RuntimeException(e);
		}
	}
	
	//For Iterable:
	//实现了Iterable接口，所以可以用foreach，不过需要一个末尾哨兵给内部类的count用，所以实现了第2个构造器
	private int size = 0;
	
	public AnimalGenerator(int size){
		this.size = size;
	}

	@Override
	public Iterator<Animal> iterator(){
		return new  AnimalIterator();
	}
	//内部类，随机生成Animal的种类的 迭代器
	private class AnimalIterator implements Iterator<Animal>{
		
		private int count = size;
		
		@Override
		public boolean hasNext() {
			return count > 0;
		}
	
		@Override
		public Animal next() {
			count--;
			return AnimalGenerator.this.RandomNext();
		}
	
		@Override
		public void remove(){
			throw new UnsupportedOperationException();
		}
	}

	public static void main(String[] args){
		
		AnimalGenerator gen = new AnimalGenerator();
		
		for(int i = 0; i < 5; i++){
			System.out.println(gen.RandomNext());
		}
		System.out.println("-------------------");
		for(Animal a : new AnimalGenerator(5)){
			System.out.println(a);
		}
	}
}

输出：
Cat default 0
Dog default 0
Cat default 1
Dog default 1
Dog default 2
-------------------
Cat default 2
Dog default 3
Dog default 4
Cat default 3
Cat default 4