I can not find the reason for the exception

Question

I am java noob and also very new to this site, so please carry me here. If I do something wrong, post it, please let me know, and I apologize in advance for everything I do, or for any bad grammar.

I need to write my own CSV parser in java that does not separate commas inside quotes. I cannot use anything related to the CSV class. 1,2,3,4 → 1 2 3 4 a, b, c ", d → ab, cd

No matter what I try, I always get an exception

import java.io.*; import java.util.*; public class csv { public static void main(String[] args) { File file = new File("csv.test"); BufferedReader buf = null; try { buf = new BufferedReader(new FileReader(file)); String str; while ((str = buf.readLine()) != null) { String[] values = null; // array for saving each split substr int c1 = 0; // counter for current position in string int c2 = 0; // counter for next space in array to save substr int c3 = 0; // location of last comma or quotation for substring creation int i = 0; // counter used later for printing while (c1 <= str.length()) { char x = str.charAt(c1); String s = Character.toString(x); if (c1 == str.length()) { values[c2] = str.substring(c3, (c1 - 1)); } else if (s == ",") { values[c2] = str.substring(c3, (c1 - 1)); c1++; c2++; c3++; } else if (s == "\"") { c1++; c3 = c1; while (s != "\"") c1++; values[c2] = str.substring(c3, (c1 - 1)); c1 = c1 + 2; c2++; c3 = c1; } else { c1++; } while (i < values.length) System.out.println("\"" + values[i] + "\""); } } } catch (Exception e) { System.out.println("Error locating test file"); } } } 

I tried to cut out all the logic and testing if this is related to the file. which reads well, so logic obeys them. I looked through it and can not find anything wrong with that. I even had a friend, and he said that everything was in order. Where is the exception thrown?

Answer 1

You do not initialize your values in this line String[] values = null; , so it will fail when you use it, i.e. in the list of values[c2] = str.substring(c3, (c1 - 1)); .

To fix the problem, initialize the values array with the appropriate length, for example. String[] values = new String[SIZE]; . You probably need to use str.length() as SIZE for the array.

Also in your else if (s == ",") comparison, you are comparing String with == , which is wrong. Instead, you can use x as else if (x == ',') .

Edit: The condition below will c1 increase unlimitedly, since you are not changing the value of str(x after correction as advised) anywhere.

Old condition:

  while (s != "\"") c1++; 

After changing as recommended (still wrong, since x does not change in the while loop):

  while (x != '"') c1++; 

Correct the logic of the loop.

Answer 2

Not related to a specific problem, but instead of s == "," you should do ",".equals(s) , as for other string equality checks.

Answer 3

This is not the reason for your exception, but, nevertheless, it is clearly incorrect:

  while (s != "\"") c1++; 

This is not true for two reasons:

• Since c1++ does not change the condition of the loop, this will be done forever.
• You use == / != To compare strings when you should use equals(...) . You seem to have made this mistake elsewhere.

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To find out what causes the exception, the first thing you need to do is print stacktrace. Add e.printStackTrace(); into the catch block.

Or better yet, modify it to just catch an IOException . Capturing an Exception is a bad idea ... if you are not going to register / output a full stack.