CODEWITHSUNDEEP
java
user3673623
user3673623

Reputation: 1925

java string index out of bound exception

It seems like a simple question but I'm wondering why if I had some String variable like this:

String name = "John";

And then I'm using the substring method like this :

System.out.print(name.substring(3,4));

it works fine but if i'd change 4 for 5 or higher I get IndexOutOfBoundsException. But as i understand indexes correct there is no 4 index as well but the outpul will be "n"

J O H N
0 1 2 3

Could someone explain such behavior? Thanks in advance!

Upvotes: 1

Views: 972

Answers (4)

Jon Skeet
Jon Skeet

Reputation: 1499790

The second parameter to substring is an exclusive upper bound - so it's allowed to be equal to the length of the string, in order to include the last character. Likewise it makes sense to allow the starting point to be "at" the end of the string, so long as the end is equal to the start, yielding an empty string.

Basically, for APIs which deal with ranges, it often makes sense to think of the indexes as being "between" characters rather than "on" them. For example:

  J O H N
 ^ ^ ^ ^ ^
 0 1 2 3 4

Both indexes have to be within the range shown, and the endIndex index must be either the same as beginIndex or to the right - then the substring is the characters between the two corresponding boundaries:

"JOHN".substring(1, 3) is "OH"

  J O H N
   ^ ^ ^
   1   3

This is exactly as documented, of course

IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

Upvotes: 7

Gherbi Hicham
Gherbi Hicham

Reputation: 2574

I think you are missunderstanding this by saying that"there is no 4 index as well but the outpul will be "n"" , the substring method counts from 1(not from 0) so your first example had nothing wrong with it because the fourth character was atually n.

Upvotes: 0

murali kurapati
murali kurapati

Reputation: 1586

substring(a,b) method of String object returns substring from index a to b-1 so substring(3,4) return only "N" i.e only index value 3. note that substring(a,a) returns always a null string.

Upvotes: 0

sp00m
sp00m

Reputation: 48807

From http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#substring(int,%20int):

Throws IndexOutOfBoundsException if the beginIndex is negative, or endIndex is larger than the length of this String object, or beginIndex is larger than endIndex.

You string's length is 4, so 4 is OK but 5 or more is KO.

Upvotes: 1

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