Strings and 2D Arrays:Reverse Each Word

public class Solution {
public static String reverseEachWord(String input){
String output="";
int index=0;
for(int i=0;i<input.length();i++){
if(input.charAt(i)==' '){
index=i+1;
output+=input.charAt(i);

}
else{
output=output.substring(0,index)+input.charAt(i)+output.substring(index);
}
}
return output;
}
}