Strings and 2D Arrays:Reverse String Word Wise

public class Solution{
public static String reverseWordWise(String input){
int end=input.length();
int i=input.length()-1;
String ans="";
while(i>=0){
if(input.charAt(i)==' '){
ans=ans+input.substring(i+1,end)+" ";
end=i;
}
i--;
}
ans+=input.substring(i+1,end);
return ans;
}
}