I am working on a project, but I cannot use any existing java data structures (ie, ArraysList, trees, etc)
I can only use arrays. Therefore, I need to dynamically update an array with new memory.
I am reading from a text file, and I pre-allocate 100 for the arrays memory:
String [] wordList;
int wordCount = 0;
int occurrence = 1;
int arraySize = 100;
wordList = new String[arraySize];
while ((strLine = br.readLine()) != null) {
// Store the content into an array
Scanner s = new Scanner(strLine);
while(s.hasNext()) {
wordList[wordCount] = s.next();
wordCount++;
}
}
Now this works fine for under 100 list items. br.readline is the buffered reader going through each line of a textfile. I have it then store each word into list and then increment my index (wordCount).
However, once I have a text file with more than 100 items, I get an allocation error.
How can I dynamically update this array (and thereby sort of reinvent the wheel)?
Thanks!
You can do something like this:
String [] wordList;
int wordCount = 0;
int occurrence = 1;
int arraySize = 100;
int arrayGrowth = 50;
wordList = new String[arraySize];
while ((strLine = br.readLine()) != null) {
// Store the content into an array
Scanner s = new Scanner(strLine);
while(s.hasNext()) {
if (wordList.length == wordCount) {
// expand list
wordList = Arrays.copyOf(wordList, wordList.length + arrayGrowth);
}
wordList[wordCount] = s.next();
wordCount++;
}
}
Using java.util.Arrays.copyOf(String[])
is basically doing the same thing as:
if (wordList.length == wordCount) {
String[] temp = new String[wordList.length + arrayGrowth];
System.arraycopy(wordList, 0, temp, 0, wordList.length);
wordList = temp;
}
except it is one line of code instead of three. :)