java字符串问题

有字符串 aaaabbbbccdeaa，要求输出为a4b4c2d1e1a2,我写的方法无法处理最后的那两个a，请高手指教！
public static void main(String[] args) {
String str = "aaaabbbbcdeaa";
char[] ss = str.toCharArray();
String s="";
char j;

for (j = 'a'; j < 'z'; j++) {
int count = 0;
for (int i = 0; i < ss.length ; i++) {
if (ss[i] == j) {
count += 1;
}

}
if(count!=0){
String sss=j+String.valueOf(count);

s+=sss;
}
}
System.out.println(s);

}

---

Java code:
/**
* 简单的压缩算法实现。<br>
* 以字符加出现的次数进行压缩，比如输入为<br>
* aaaabbbbccdeaa<br>
* 输出为<br>
* a4b4c2d1e1a2
*
* @author Java人(javaren.org)
*/
public class TestCompress {
/**
* @param args
*/
public static void main(String[] args) {
String str = "aaaabbbbccdeaa";
char[] cs = str.toCharArray();
char last = 0;
int num = 0;
for (char c : cs) {
if (last == 0) {
last = c;
System.out.print(last);
num = 1;
} else {
if (c == last) {
num++;
} else {
System.out.print(num);
last = c;
System.out.print(last);