用Java程序写出 农场有一头母牛,每年生一头小母牛,小牛5岁可生小牛,20年后有多少头牛

用Java程序写出 农场有一头母牛,每年生一头小母牛,小牛5岁可生小牛,20年后有多少头牛

public class Test {


public static void main(String[] args) throws IOException {
List cows = new ArrayList();
Cow curCow = new Cow();
curCow.setAge(5);
cows.add(curCow);
System.out.println(cows.size());
for (int i = 1; i <= 20; i++) {
for (int j = 0; j < cows.size(); j++) {
curCow = cows.get(j).getCow();
if(null!=curCow)
cows.add(curCow);
}
}
System.out.println(cows.size());
}
}

class Cow{
private int age = 1;
public Cow getCow(){
if(age<5){
this.age++;
return null;
}
this.age++;
return new Cow();
}
public void setAge(int age){
this.age = age;
}
}

public static void main(String[] args) {
  int[] c = new int[25];
  c[1] = 1;
  for (int i=2;i<=20;i++){
    c[i] = c[i-1] + (i-5 > 0 ? c[i-5] : 0);
  }
  System.out.println(c[20]);
}