为何在主函数创建对象，调用方法的时候会出错？？？

package com.imooc11;import java.util.ArrayList;import java.util.HashSet;import java.util.List;import java.util.Set;public class Puke {	//创建扑克牌属性（没想到）	public String num;	public String color;	public String str1[]={" "};	public String str2[]={" "};public List<Puke>pukes;  //定义存放扑克容器//对象实例化public Puke(String color,String num){	this.num=num;	this.color=color;	this.pukes=new ArrayList<Puke>();}//创建52张扑克牌public void creatPuke(){	String str1[]={"黑桃","红桃","梅花","方片"};	String str2[]={"2","3","4","5","6","7","8","9","10","J","Q","K","A"};	for(int i=0;i<str1.length;i++){		for(int j=0;j<str2.length;j++){			Puke pk=new Puke(str1[i],str2[j]);			pukes.add(pk);		}	}}/* * 遍历扑克牌 */public void forPuke(){	System.out.println("******52张扑克牌******");	for (Puke pk:pukes){		System.out.println(pk.color+":"+pk.num);	}}	public static void main(String[] args) {		// TODO Auto-generated method stub		Puke pk=new Puke();			}}