vector和hashMap的结合使用，比较棘手！

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vector和hashMap的结合使用，比较棘手！5

我自己创建了几个hashMap，然后想把这些map放到vector中，可是只要一添加map到vector中，就会报空指针，也不知道是怎么出来的，我也用上了泛型，哪位大哥大姐知道，给看看问题在哪，下面是代码！
import java.util.HashMap;
import java.util.Vector;

public class MapTst {

static Vector<HashMap<Integer, String>> vec=null;

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Vector<String> vecstr=null;
MapTst.initMap();
for(int i=1;i<=9;i++){
String str="";
boolean rtn = recursiveFind(1,vec,1,str);
if(rtn==true) vecstr.add(str);
}
System.out.println(vecstr.size());
}

static void initMap(){
HashMap<Integer, String> map1 = new HashMap<Integer,String>();
map1.put(1,"dxd");
map1.put(2,"wlp");
map1.put(3,"gj");
map1.put(4,"chenxi");
map1.put(5,"tiananmen");
map1.put(6,"renmin");
map1.put(7,"zuqiu");
map1.put(8,"fengsaka");
map1.put(9,"lanqiu");
//Vector vec = null;
// vec.add(map1);
vec.add(0,map1);
//vec.addElement(map1);

HashMap<Integer, String> map2 = new HashMap<Integer,String>();
map2.put(1,"gugong");
map2.put(2,"yonghegong");
map2.put(3,"dianmen");
map2.put(4,"xizhimen");
map2.put(5,"jianguomen");
map2.put(6,"chaoyangmen");
map2.put(7,"dongzhimen");
map2.put(8,"qianmen");
map2.put(9,"fuchengmen");
map2.put(10,"deshengmen");

// vec.add(map2);
vec.addElement(map2);
HashMap<Integer, String> map3 = new HashMap<Integer,String>();
map3.put(1,"1");
map3.put(2,"2");
map3.put(3,"3");
map3.put(4,"4");
map3.put(5,"5");
map3.put(6,"6");
map3.put(7,"7");
map3.put(8,"8");
map3.put(9,"9");
map3.put(9,"10");

// vec.add(map3);
vec.addElement(map3);

HashMap<Integer, String> map4 = new HashMap<Integer,String>();
map4.put(1,"a");
map4.put(2,"b");
map4.put(3,"c");
map4.put(4,"d");
map4.put(5,"e");
map4.put(6,"f");
map4.put(7,"g");
map4.put(8,"h");
map4.put(9,"i");
map4.put(9,"j");

HashMap<Integer, String> map5 = new HashMap<Integer,String>();
map5.put(1,"11");
map5.put(2,"22");
map5.put(3,"33");
map5.put(4,"44");
map5.put(5,"55");
map5.put(6,"66");
map5.put(7,"77");
map5.put(8,"88");
map5.put(9,"99");
map5.put(9,"111");

vec.addElement(map4);
vec.addElement(map5);
// vec.add(map4);
// vec.add(map5);
//vec.a
}

static boolean recursiveFind(Integer k, Vector<HashMap<Integer, String>> vec, Integer i,String str){
if(i>vec.size())return false;

if(vec.get(i).containsKey(k))
{
str += k.toString();
recursiveFind(++k,vec,++i,str);
}
else
{
return false;
}

return true;
}

}

我用了add，addElement都不行，不知道为何？请大家看看，我主要是想用这个东西来实现后面的递归算法，郁闷啊！分开用vector和hashMap都没问题，居然结合着用就报这个怪问题！
问题补充：
呵呵，我搞定了，确实是大家说的那个原因，我是想实现一个算法：
ABCDE共5个位置，如果A位置出现0的话，那么B位置就必须是1，C位置必须是2，类推。
后来用了个递归来实现的，不知道大家有没有更好的方法，按照我的算法，也能实现，不过是递归，不太好！

问题补充：
这里怎么结贴啊，有没有像csdn那样的，我想结贴，散分！

J2ME