Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

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

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?

like image 572
siaooo Avatar asked Dec 08 '12 21:12

siaooo


3 Answers

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())
like image 52
Tomasz Nurkiewicz Avatar answered Nov 03 '22 19:11

Tomasz Nurkiewicz


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.

like image 35
Eric Avatar answered Nov 03 '22 19:11

Eric


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]
}
like image 31
Petar Ivanov Avatar answered Nov 03 '22 18:11

Petar Ivanov