https://codingbat.com/prob/p190570 - boolean and String

[Pedro Esgueira]

Hi,

On codingbat exercise https://codingbat.com/prob/p190570

Questions:
1) I'm getting the error message incompatible types: boolean cannot be converted to java.lang.String.  I've researched a bit, but I'm not entirely sure why I'm apparently trying to convert a boolean to a String.
2) Also I interpreted they were asking me to code for the following checks:  
- the string not to be empty
- the n to be within a certain range
but their solution has no conditions.

The problem reads:
"Given a non-empty string and an int n, return a new string where the char at index n has been removed. The value of n will be a valid index of a char in the original string (i.e. n will be in the range 0..str.length()-1 inclusive).

missingChar("kitten", 1) → "ktten"
missingChar("kitten", 0) → "itten"
missingChar("kitten", 4) → "kittn"

My solution:

public String missingChar(String str, int n) {
  int a = str.length();
  int b = a-1;
  if(a>=1 && n<=b) {
    String newString = str.substring(0, n) + str.substring(n+1);
    return newString;
  }
  else
    return false;
}

Their solution:

public String missingChar(String str, int n) {
  String front = str.substring(0, n);
  
  // Start this substring at n+1 to omit the char.
  // Can also be shortened to just str.substring(n+1)
  // which goes through the end of the string.
  String back = str.substring(n+1, str.length());
  
  return front + back;
}

[Piet Souris]

hi Pedro,

your method definition says that a String will be returned (line 1). However, in line 9 you return a boolean. That is not a String, so the compiler gives you that error

But you do not need that checking at all. If you look at the constraints of the exercise, they guarantee that the input will be valid. So, in particular, the String cannot be empty, since then no index would be valid, and the index is always minimal 0 and maximal s.length() - 1.

[Pedro Esgueira]

Hi Piet, thanks

Of course! The method type needs to match the return type.. *facepalm. I was thinking that the error was in my boolean logic... but its the return type. Got it.