Encode Decode String

/**
Encode and Decode Strings
Design an algorithm to encode a list of strings to a string. The encoded string is then sent over the network and is decoded back to the original list of strings.
Machine 1 (sender) has the function:
string encode(vector<string> strs) {
  // ... your code
  return encoded_string;
}
Machine 2 (receiver) has the function:
vector<string> decode(string s) {
  //... your code
  return strs;
}
So Machine 1 does:
string encoded_string = encode(strs);
and Machine 2 does:
vector<string> strs2 = decode(encoded_string);
strs2 in Machine 2 should be the same as strs in Machine 1.
Implement the encode and decode methods.
Note: The string may contain any possible characters out of 256 valid ascii characters. Your algorithm should be generalized enough to work on any possible characters.
Do not use class member/global/static variables to store states. Your encode and decode algorithms should be stateless.
Do not rely on any library method such as eval or serialize methods. You should implement your own encode/decode algorithm.

Tips:
input string is separated by slash:

The encoded form of strings is length + '/' +str + length + '/' + str.
If you say, there is a '/' in a str. Then it is counted for the length of that str but the added slash is not.
For "ab/cd", the encoded one should be "5/ab/cd". The decode function will read the length first, then skip the slash between '5' and 'a', starting from the next character and get the substring of that length which is "ab/cd".
*/
public class EncodeDecodeString{

//encoder
String encode(List<String> ss){
StringBuilder sb = new StringBuilder();
for(String s:ss){
sb.append(s.length()).append("/").append(s);
}
return sb.toString();
}

//decoder
List<String> decode(String s){
int i = 0;
List<String> res = new ArrayList<String>();
while(i<s.length()){
int slash = s.indexOf('/', i);
int len = Integer.valueOf(s.substring(i, slash));
String text = s.substring(slash+1, slash+1+len);
res.add(text);
i = slash+1+len;
}
return res;
}
}