// -- grow the array to requested capacity c, throw an exception if the requested // capacity c is smaller than the current size public void ensureCapacity(int c) throws IllegalArgumentException;

I'm having trouble understanding how to write this

This is what I have so far

public void ensureCapacity(int c) throws IllegalArgumentException { if (size() >= data.length) { @SuppressWarnings("unchecked") T[] newData = (T[]) (new Object[size * 2 + 1]); System.arraycopy(data, 0, newData, 0, size); data = newData; } else { throw new IllegalArgumentException(); } }

Running code for Java