软件大赛题目----（第九个）求牛的数目

package com.bird.software;

import java.util.ArrayList;
import java.util.List;

public class Cow {
	private int age;
	
	public Cow afterYears(){
		age++;
		return age > 2 ? new Cow() : null;
	}
	
	public static void showTotalCowNum(int n){
		List<Cow> list = new ArrayList<Cow>();
		list.add(new Cow());
		
		for(int i = 0; i < n; i++){
			int cowCount = list.size();
			for(int j = 0; j < cowCount; j++){
				Cow cow = list.get(j).afterYears();
				if(cow != null){
					++cowCount;
					list.add(cow);
				}
			}
		}
		
		System.out.println(n+"年后，共有："+list.size()+"头牛");
	}
	
	
	public static void main(String[] args){
		showTotalCowNum(5);
	}
}