Java实现：工厂有一头母牛,一年生一头小母牛,小母牛五年后可以生小牛,问20年工厂有多少头牛?

文件Mooooo.java如下：
import java.util.ArrayList;
public class Mooooo {
public static void main(String[] args) {
ArrayList cows = new ArrayList();
cows.add(new Cow(4));

for (int i = 0; i < 20; i++) {
ArrayList newCows = new ArrayList();
for (Cow cow : cows) {
cow.happyBirthday(newCows);
}
cows.addAll(newCows);
}

System.out.println("二十年共有牛 " + cows.size() + " 头.");
}
}
文件Cow.java如下：
import java.util.ArrayList;
/**
* 母牛类
*/
public class Cow {
private int age = 0;
public Cow(int age) {
this.age = age;
}
public void happyBirthday(ArrayList cows) {
age++;
if (age >= 4) {
cows.add(new Cow(0));
}
}
}
计算出结果是907头牛,已调试成功,若有不明之处可联系我.