How can I get a string's length in Java without String API methods?

Question

Possible Duplicate:
String length without using length() method in java

I need to get the length of a string (no of characters present) in Java using a for loop and without using any methods like length().

import java.io.*;
import java.util.*;

public class reversestring

{
    public static void main(String arg[])throws IOException

    {
     String s;
     int i=0,j=0,k=0;
     DataInputStream in=new DataInputStream(System.in);
     System.out.println("Enter ur string : ");
     s=in.readLine();
     char ar[]=s.toCharArray();
     System.out.println("Length of the string is : ");

     for(j=ar[i];j!='\0';i++)
     {

         k++;

     }
     System.out.println(+k);
    }
}

I wrote this program, but I am not getting the answer. What is wrong with it?

As you "cannot" use `length()`.. should this be tagged "homework" ? — Nanne, Feb 10 '11 at 14:44
@Nanne: according to [this](http://meta.stackexchange.com/questions/10811/how-to-ask-and-answer-homework-questions) the homework-tag (together with other meta-tags) is discouraged. — Joachim Sauer, Feb 10 '11 at 14:47
Possible duplicate: http://stackoverflow.com/questions/2910336/string-length-without-using-length-method-in-java/2910357#2910357 — aioobe, Feb 10 '11 at 14:49
Ha, ha, ha, ha ... ! Sorry, sorry, thousand apologies. Could not resist the humour. — Blessed Geek, Feb 10 '11 at 14:49
Not a real question. You check the length of a String in Java using the length() method, and there is no defensible reason to do it any other way. — Christoffer Hammarström, Feb 10 '11 at 14:51
@joachim-sauer : That's not what I read in that link; it's about how to _respond_ to those questions. I was suggesting it, because it would help understanding the question: otherwise I'd ask to specify why `length()` couldn't be used. If there is some strange reason for that, we might need to take that into account too. But as it is probably homework, we can just take it as a given. So it's not "becasue I don't want to answer that!" but more "what is going on?". See other comments :D — Nanne, Feb 10 '11 at 14:51

score 6 · Answer 1 · answered Feb 10 '11 at 14:50

6

This has been asked before. Here's my favorite answer:

str.lastIndexOf("")

(which probably even runs in constant time, as opposed to the other answers.)

answered Feb 10 '11 at 14:50

aioobe

413,195
112
811
826

score 5 · Answer 2 · answered Feb 10 '11 at 14:44

5

The following .length is not a method.

int length = s.toCharArray().length

answered Feb 10 '11 at 14:44

Peter Lawrey

525,659
79
751
1,130

nor is it a property of the String API. Great workaround. – Andy Feb 10 '11 at 14:56
3

What's the "String API"? Why wouldn't `toCharArray` be included in that definition? – aioobe Feb 10 '11 at 15:10
You can't access the String without using the API, unless you use reflection to get the `length` field. – Peter Lawrey Feb 10 '11 at 19:13

score 1 · Answer 3 · answered Feb 10 '11 at 14:42

1

Java isn't C, thus you can't treat Java strings as C strings and you can't expect C methods to work in Java. In particular, Java strings aren't null-terminated.

The 'correct' way would be to use length (either a string method, or an array property), but, since you don't want, you could employ 'for each' loop.

for (char c in charArray) {
    ++count;
}

It feels not good, though.

answered Feb 10 '11 at 14:42

Nikita Rybak

67,365
22
157
181

The task itself is completely meaningless in the first place, which makes it pretty impossible to give a "good" answer. Having said that: this only hides the `.length` behind some syntactic sugar ;-) – Joachim Sauer Feb 10 '11 at 14:44
@Joachim I completely agree, I would never let this code pass review, let alone use it myself :) – Nikita Rybak Feb 10 '11 at 14:45

score 1 · Answer 4 · answered Feb 10 '11 at 15:05

1

a functional guy would answer

len(str)
   return str.isEmpty() ? 0 : 1+len(str.substring(1));

answered Feb 10 '11 at 15:05

irreputable

44,725
9
65
93

1

why +1? I was being sarcastic... – irreputable Feb 10 '11 at 15:32

score 1 · Answer 5 · answered Feb 10 '11 at 15:12

1

int counter;
String s = "something";

try{
    for(counter=0; s.charAt(counter); counter++);       

}catch(Exception e){
   //ArrayIndexOutOfBoundsException
   System.out.println("Length: " + counter);
}

answered Feb 10 '11 at 15:12

David

21
1

score 0 · Answer 6 · answered Feb 10 '11 at 14:46

0

I believe Java's String.toCharArray() returns an array that is not null-terminated, so looking for a null character would not work.

answered Feb 10 '11 at 14:46

irritate

7,350
1
17
11

score 0 · Answer 7 · answered Feb 10 '11 at 15:32

0

I can't believe all the other answers are using the String API, although the title of this question indicates that's not allowed :-P

I came up with this:

System.out.println(new StringReader("stackoverflow").skip(Long.MAX_VALUE));

answered Feb 10 '11 at 15:32

Adriaan Koster

15,870
5
45
60

I strongly suspect that StringReader is using the String API behind the scenes. You are simply delegating the use of the API to it. – ILMTitan Feb 10 '11 at 16:50

How can I get a string's length in Java without String API methods?

7 Answers7