Java string index out of range

Question

So I get that String index out of range means that I'm exceeding the range of a collection, but I'm not quite sure how I'm doing that with my code.

This code is supposed to read from a text file which contains 3 ints( the first two being what are relevant to this as the number of rows and number of columns respectively) and then a series of characters. So first it reads and saves the first three numbers, then converts the rest of the file to String. It then follows this up by setting up an array of chars with the dimensions of the text file and then filling in those values with the characters of the text file character by character.

However, when I try to print out the code, I encounter the string index out of range error and cannot find the problem.

This is the code:

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

public class SnakeBox {
// instance variables
  private char[][] box;
  private int snakeCount;
  private int startRow, startCol;
  private int endRow, endCol;
    private int rows, cols, snakes;
  Scanner keyboard = new Scanner(System.in);

/** Create and initialize a SnakeBox by reading a file.
    @param filename the external name of a plain text file
*/
  public SnakeBox(String fileName) throws IOException{
     Scanner infile = new Scanner(new FileReader(fileName));


     int count = 0;
     String s = "";
     rows = infile.nextInt();
     cols = infile.nextInt();
     snakes = infile.nextInt();
        infile.nextLine();
     box = new char[rows][cols];
     while (infile.hasNext()) {
        s += infile.next();
     }
     for (int i = 0; i < rows; i++) {

        for (int j = 0; j < cols; j++) {
           count++;
           char c = s.charAt(count);           
           box [i][j] = c;
        }
     }
  }

The text file is :

    16 21 4
+++++++++++++++++++++
+                   +
+         SSSSS     +
+    S   S          +
+    S    SS        +
+    S      S       +
+ S  S       SS     +
+  SS  S            +
+     S             +
+    S  SSSSSS      +
+   S         S     +
+  S           S    +
+ S     SSS   S     +
+      S     S      +
+       SSSSS       +
+++++++++++++++++++++

Thank you.

gefei · Accepted Answer · 2013-04-05 09:33:30Z

6

change

count++;
char c = s.charAt(count);

to

char c = s.charAt(count);   
count++;

EDIT: another issue is that Scanner.next() returns the next token, ignoring all spaces. See the answer of Achintya Jha

edited Apr 5, 2013 at 9:33

answered Apr 5, 2013 at 9:05

gefei

20k9 gold badges54 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

John Snow Over a year ago

Indeed this will cause a problem when you're on the last index. Say you are on index 10(which is last), you will then try to get charAt() index 11 which do not exist. Great spotted

user2248256 Over a year ago

Ah, thank you, silly mistake. However, running the file through again still leaves me with a string index out of bounds exception at the same spot.

gefei Over a year ago

@user2248256 hmm. i'd try to print out the value of s, the length of it, and then the value of count to see what's the matter

Achintya Jha · Accepted Answer · 2013-04-05 09:36:05Z

2

The problem is not what stated above: In the given file there are nearly 59 tokens that will be equals to 117 characters total (I counted manually) . Whereas the maximum value of count will reach 21*16 =336.

If the input file named "infile.dat" has the following format:

Hello There 1234
CSstudents goodbye 6556

it has six tokens that we can read in using the following code:

while (filein.hasNext()) {      // while there is another token to read
    String s = filein.next();   // reads in the String tokens "Hello" "CSstudents" 
    String r = filein.next();   // reads in the String tokens "There" "goodbye"
    int x = filein.nextInt();   // reads in the int tokens 1234  6556 

}

Notice how the Scanner object skips over all white-space characters to the start of the next token. So my suggestion is to use Scanner#hasNextLine() & Scanner#nextLine()

while (infile.hasNextLine) {
    s += infile.nextLine();
}

edited Apr 5, 2013 at 9:36

answered Apr 5, 2013 at 9:19

Achintya Jha

12.9k2 gold badges31 silver badges40 bronze badges

4 Comments

Alex Over a year ago

Check the doc docs.oracle.com/javase/1.5.0/docs/api/java/util/… Like Achintya said next() returns a token. All the whitespaces in your file are ignored.

user2248256 Over a year ago

Ah thank you, this is a big problem, how would I be able to save the empty spaces in my array as well?

Alex Over a year ago

I never used the Scanner, but readLine might help since it is not reading tokens as far as I understand the doc. while (scanner.hasNextLine()) { someString = someString + scanner.nextLine(); } Afterwards convert the String to your array.

user2248256 Over a year ago

Thank you very much everyone. Changing it to read the line instead of next token fixed it, I had a misunderstanding of what next() did. Thanks also to the other answer as that was also a problem.

Collectives™ on Stack Overflow

Java string index out of range

2 Answers 2

3 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related