Reason for subtracting substring()'s endIndex by 1 [duplicate]

Question

Possible Duplicate:
why from index is inclusive but end index is exclusive?

substring() method => String substring(int beginIndex, int endIndex)

Description:

Returns a new string that is a substring of this string. The first integer argument specifies the index of the first character. The second integer argument is the index of the last character - 1.

Take a look at the following code:

String anotherPalindrome = "Niagara. O roar again!"; 
String roar = anotherPalindrome.substring(11, 15); 

Output: roar

Now, if the JVM didn't substract int endIndex by one, we could just use substring(11,14) instead, wouldn't that be much more convenient and less error-prone (human side)? Had you not read the description carefully, you might just ended up scratching your head for half an hour (like I did) when you thought that endIndex is just the normal index. What's the reason for the Java language creators to subtract it by one?

Answer 1

It has several advantages:

s.substring(0, s.length())

is always correct. Also:

s.substring(i, j)

The size of resulting string is always j - i. More specifically s.substring(0, j) will always return j characters. Finally this means that if you want to take n characters after index i you simply say:

s.substring(i, i + n)

It's also easier to extract suffix of a string (last n characters):

s.substring(s.length() - n, s.length())

For example extracting file extension:

s.substring(s.indexOf('.') + 1, s.length())

Answer 2

Think of it as numbering the gaps between letters, not the letters themselves:

 N i a g a r a . _ O  _  r  o  a  r  _  a  g  a  i  n  !
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Clearly, roar is the substring between 11 and 15.

Answer 3

This is the same question as:

"Why do the arrays in Java start at 0 and not at 1".

Indeed, since the arrays start at 0 you usually write:

for(int i = 0; i < ar.length; i++)

similarly if you want a substring starting from start and ending at end you would use something like:

for(int i = start; i < end; i++)
{
    //get ar[i]
}