CareerCup

In Q1.5, solution compressBetter, since StringBuffer does not have a prefix size, do we still need to check the size of the compressed string before building it up?
we can compare the size of the buffer with the original string while building up the new string. If the length of the new string exceeds the original one, then return the original string.

Here's my code:
public static String compress(String str) {
if(str.length()<=2) {
return str;
}
StringBuffer mystr = new StringBuffer();
char last = str.charAt(0);
int count = 1;
for(int i=0;i<str.length();i++){
if(str.charAt(i) == last) {
count++;
} else {
mystr.append(last);
mystr.append(count);
last = str.charAt(i);
count =1;
}
if(mystr.length() >= str.length()) {
return str;
}
}
mystr.append(last);
mystr.append(count);
return mystr.toString();
}