java substring(1,2) issue

public boolean mixStart(String str) {
  if ((str.substring(1,3)).equals("ix")){
  return true;
  }
  return false;
}

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when i tried as above i have some test cases failing as below


Expected      Run            
mixStart("mix snacks") → true      true      OK         
mixStart("pix snacks") → true      true      OK         
mixStart("piz snacks") → false      false      OK         
mixStart("nix") → true      true      OK         
mixStart("ni") → false      Exception:java.lang.StringIndexOutOfBoundsException: String index out of range: 3 (line number:2)      X         
mixStart("n") → false      Exception:java.lang.StringIndexOutOfBoundsException: String index out of range: 3 (line number:2)      X         
mixStart("") → false      Exception:java.lang.StringIndexOutOfBoundsException: String index out of range: 3 (line number:2)      X       



I do not see any specific requirement for small strings of 2 or 1 etc characters in the challenge.


Return true if the given string begins with "mix", except the 'm' can be anything, so "pix", "9ix" .. all count.

mixStart("mix snacks") → true
mixStart("pix snacks") → true
mixStart("piz snacks") → false

Please advise

return str.indexOf("ix") == 1;

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what is meaning of above line? Does it simply check if 'ix' is there in the given string 'str'?
Please advise

I do not see any specific requirement for small strings of 2 or 1 etc characters in the challenge.

It's not spelled out, but they are sending in some short strings to test the behavior.

Give this a try and then see if you can see why it fixed it:

public boolean mixStart(String str) {
  if (str.length() > 2 && (str.substring(1,3)).equals("ix")){
  return true;
  }
  return false;
}

And this line:

str.indexOf("ix") == 1;

checks to see if "ix" is within the string...and also if it's in position 1.  Can you see how that would solve this too?

Doug

public boolean mixStart(String str) {
  if (str.length() > 2 && (str.substring(1,3)).equals("ix")){
  return true;
  }
  return false;
}

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solving all test cases


Also

public boolean mixStart(String str) {
    return str.indexOf("ix") == 1;
}

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above also passing all test cases

And this line:
str.indexOf("ix") == 1;

checks to see if "ix" is within the string...and also if it's in position 1.

ix position check 1 means checking the starting position of i right(which is the first letter in ix?)
Please advise

Do you understand the documentation for the indexOf function?
http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#indexOf%28java.lang.String%29

I was reading it now.

The returned index is the smallest value k for which:

 k >= fromIndex && this.startsWith(str, k)

what it means by above line?

ix position check 1 means checking the starting position of i right(which is the first letter in ix?)

Yes that's right.

It's the position in the string where the substring ("ix") starts.

k >= fromIndex
means k is greater than or equal to k >= fromIndex

this.startsWith(str, k) is documented here:
http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#startsWith%28java.lang.String,%20int%29

The returned index is the smallest value k for which:
means that there is no smaller value for which this is true
i.e. if there is more than one value which satisfies it, we choose the smallest one.

i need to read more

i never used regular expressions. I wonder i can do programming without knowing regular expression? May be it is easy to learn regular expression with java background. please advise