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())