My add and remove program

Question

I am asked to create an add method with the following rules:
When adding new elements, check to ensure there is room in the array data. If there is no unused array index, grow the array by delta elements. When removing existing elements, shrink the array by delta elements whenever there is room to add more than delta elements. In other words, leave no more than delta empty array locations at any time. The array must have from 0 through delta empty indexes at all times. The following assertions must pass.
This add method must work for any data type. And so far the method that I have create is:
public boolean add(E element) {
    boolean result = false;
    Object[] temp = new Object[data.length+delta];
        if (data.length == n){
            for (int i = 0; i<data.length; i++){
                temp[i] = data;
data = temp;
for (int i=0; i<data.length; i++){
if (data[i].equals(element))
result = false;
else{
n++;
data[n-1] = element;
result = true;
return result;
The problem with this code is that when I try to add an interger it always gives me a null point exception because all the value in the array are set as null the very first time, how do I get this method to work the way it's suppose to be??

Answer 1

okay guys, so here's now for my remove method:
public boolean remove(E element) {
          boolean result = true;
          int position = 0;
          int count = 0;
          for (int i = 0; i <= n; i++) {
               if (element.equals(data)) {
                    result = true;
                    position = i;
          if (result == true) {
               for (int j = position; j < n - 1; j++) {
                    data[position] = data[position + 1];
               data[n - 1] = null;
               n--;
          for (int k = 0; k< data.length; k++) {
               if (data[k] == null)
                    count++;
          if (count>=delta){
               Object[] temp = new Object[data.length - (count-delta)];
               for (int m = 0; m<temp.length; m++)
                    temp[m] = data[m];
               data = temp;     
          return result;
This method wont work according to the rules:
When removing existing elements, shrink the array by delta elements whenever there is room to add more than delta elements. In other words, leave no more than delta empty array locations at any time. The array must have from 0 through delta empty indexes at all times. The following assertions must pass.
why is that?? can someone help me?
My teacher has provided me with this test method:
@Test
     public void testGrowAndShrink() {
       Set<Integer> ints = new ArraySet<Integer>(5, 10);
       for (int i = 1; i <= 20; i++)
         ints.add(i);
       assertEquals(20, ints.size());
       // Array has now grown twice by 10 elements (capacity went from 5 to 25)
       assertEquals(25, ints.capacity());
       for (int i = 1; i <= 4; i++)
         ints.remove(i);
       assertEquals(16, ints.size());
       assertEquals(25, ints.capacity());
       ints.remove(5);
       // Array shrunk by 10 elements
       assertEquals(15, ints.size());
       assertEquals(15, ints.capacity());
     } and it didn't pass the assertEquals(15, ints.capacity());
why???
Message was edited by:
aditya15417
Message was edited by:
aditya15417