Probelm with String.split() in java

Question

What I am trying to do is read a .java file, and pick out all of the identifiers and store them in a list. My problem is with the .split() method. If you run this code the way it is, you will get ArrayOutOfBounds, but if you change the delimiter from "." to anything else, the code works. But I need to lines parsed by "." so is there another way I could accomplish this?

import java.io.BufferedReader;

import java.io.FileNotFoundException;

import java.io.FileReader;

import java.io.IOException;

import java.util.*;



public class MyHash {

private static String[] reserved = new String[100];

private static List list = new LinkedList();

private static List list2 = new LinkedList();

public static void main (String args[]){
  Hashtable hashtable  = new Hashtable(997);
  makeReserved();
  readFile();                                                 
  String line;
  ListIterator itr = list.listIterator();
  int listIndex = 0;
  while (listIndex < list.size()) {                                       

        if (itr.hasNext()){
          line = itr.next().toString();
          //PROBLEM IS HERE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
          String[] words = line.split(".");  //CHANGE THIS AND IT WILL WORK
          System.out.println(words[0]);      //TESTING TO SEE IF IT WORKED
        }
        listIndex++;
        }
  }









public static void readFile() {
    String text;
    String[] words;
    BufferedReader in = null; 
    try {
        in = new BufferedReader(new FileReader("MyHash.java")); //NAME OF INPUT FILE


    } catch (FileNotFoundException ex) {
        Logger.getLogger(MyHash.class.getName()).log(Level.SEVERE, null, ex);
    }
    try {
        while ((text = in.readLine()) != null){
        text = text.trim();
        words = text.split("\\s+");
        for (int i = 0; i < words.length; i++){
            list.add(words[i]);
        }
        for (int j = 0; j < reserved.length; j++){
            if (list.contains(reserved[j])){
                list.remove(reserved[j]);
            }
        }


    }

    } catch (IOException ex) {
        Logger.getLogger(MyHash.class.getName()).log(Level.SEVERE, null, ex);
    }
    try {
        in.close();
    } catch (IOException ex) {
        Logger.getLogger(MyHash.class.getName()).log(Level.SEVERE, null, ex);
    }

}



public static int keyIt (int x) {
   int key = x % 997;
   return key;
}

public static int horner (String word){
    int length = word.length();
    char[] letters = new char[length];

    for (int i = 0; i < length; i++){
        letters[i]=word.charAt(i);
    }

    char[] alphabet = new char[26];
    String abc = "abcdefghijklmnopqrstuvwxyz";

    for (int i = 0; i < 26; i++){
        alphabet[i]=abc.charAt(i);
    }

    int[] numbers = new int[length];
    int place = 0;
    for (int i = 0; i < length; i++){
        for (int j = 0; j < 26; j++){
            if (alphabet[j]==letters[i]){
                numbers[place]=j+1;
                place++;

            }
        }
    }

    int hornered = numbers[0] * 32;

    for (int i = 1; i < numbers.length; i++){

        hornered += numbers[i];
        if (i == numbers.length -1){
            return hornered;
        }
        hornered = hornered % 997;
        hornered *= 32;
    }
    return hornered;
}

public static String[] makeReserved (){
    reserved[0] = "abstract";
    reserved[1] = "assert";
    reserved[2] = "boolean";
    reserved[3] = "break";
    reserved[4] = "byte";
    reserved[5] = "case";
    reserved[6] = "catch";
    reserved[7] = "char";
    reserved[8] = "class";
    reserved[9] = "const";
    reserved[10] = "continue";
    reserved[11] = "default";
    reserved[12] = "do";
    reserved[13] = "double";
    reserved[14] = "else";
    reserved[15] = "enum";
    reserved[16] = "extends";
    reserved[17] = "false";
    reserved[18] = "final";
    reserved[19] = "finally";
    reserved[20] = "float";
    reserved[21] = "for";
    reserved[22] = "goto";
    reserved[23] = "if";
    reserved[24] = "implements";
    reserved[25] = "import";
    reserved[26] = "instanceof";
    reserved[27] = "int";
    reserved[28] = "interface";
    reserved[29] = "long";
    reserved[30] = "native";
    reserved[31] = "new";
    reserved[32] = "null";
    reserved[33] = "package";
    reserved[34] = "private";
    reserved[35] = "protected";
    reserved[36] = "public";
    reserved[37] = "return";
    reserved[38] = "short";
    reserved[39] = "static";
    reserved[40] = "strictfp";
    reserved[41] = "super";
    reserved[42] = "switch";
    reserved[43] = "synchronize";
    reserved[44] = "this";
    reserved[45] = "throw";
    reserved[46] = "throws";
    reserved[47] = "trasient";
    reserved[48] = "true";
    reserved[49] = "try";
    reserved[50] = "void";
    reserved[51] = "volatile";
    reserved[52] = "while";
    reserved[53] = "=";
    reserved[54] = "==";
    reserved[55] = "!=";
    reserved[56] = "+";
    reserved[57] = "-";
    reserved[58] = "*";
    reserved[59] = "/";
    reserved[60] = "{";
    reserved[61] = "}";




    return reserved;
}

}

Answer 1

String.split() takes a regex, and '.' has special meanings for regexes.

You (probably) want something like:

String[] words = line.split("\\.");

Answer 2

The argument to split is a regular expression. "." matches anything so your delimiter to split on is anything.

Answer 3

Have you tried escaping the dot? like this:

String[] words = line.split("\\.");

Answer 4

The argument to split is a regular expression. The period is a regular expression metacharacter that matches anything, thus every character in line is considered to be a split character, and is thrown away, and all of the empty strings between them are thrown away (because they're empty strings). The result is that you have nothing left.

If you escape the period (by adding an escaped backslash before it), then you can match literal periods. (line.split("\\."))

Answer 5

You might be interested in the StringTokenizer class. However, the java docs advise that you use the .split method as StringTokenizer is a legacy class.

Answer 6

If performance is an issue, you should consider using StringTokenizer instead of split. StringTokenizer is much much faster than split, even though it is a "legacy" class (but not deprecated).