How can we dynamically allocate and grow an array

Question

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!

Answer 1

you can not increase array size dynamically better you copy into new array. Use System.arrayCopy for that, it better than copying each element into new array. For reference Why is System.arraycopy native in Java?.

private static Object resizeArray (Object oldArray, int newSize) {
   int oldSize = java.lang.reflect.Array.getLength(oldArray);
   Class elementType = oldArray.getClass().getComponentType();
   Object newArray = java.lang.reflect.Array.newInstance(
         elementType, newSize);
   int preserveLength = Math.min(oldSize, newSize);
   if (preserveLength > 0)
      System.arraycopy(oldArray, 0, newArray, 0, preserveLength);
   return newArray;
}