if statement - Java control flow -

i'm working on notreplace problem on codingbat. i've identified section of code wrong have not idea why. when notreplace("this right") called output: "thtest test right". why following section of code run?

    else if (!(character.isletter(i-1)) && i+2<len && !(character.isletter(i+2))){ newstr += "test"; i++; }   

when i==2, charat(i-1)=='h' first condition not satisfied, since h letter 'is' still gets replaced 'test'. appreciated. full code below:

    public string notreplace(string str) {     string newstr = "";     string in = "is not";     int len = str.length();       (int i=0; i<len; i++){       if (str.substring(i,math.min(i+2,len)).equals("is")){         if (i==0 && i+2<len && !(character.isletter(i+2))){         newstr += in;         i++;        }         else if (i+2==len && !(character.isletter(i-1))){         newstr += in;         i++;         }        else if (!(character.isletter(i-1)) && i+2<len && !(character.isletter(i+2))){         newstr += "test";         i++;         }        else newstr += str.charat(i);       }        else newstr += str.charat(i);      }      return newstr;     } 

character.isletter(i - 1) when i =2 character.isletter(i-1) --> character.isletter(1)

so it's false , because 1 not letter . first condition !character.isletter(i - 1) true.you have missed charat(i-1) part

you should use

!character.isletter(charat(i-1))