public class MaxHeapextends Comparablesuper T>> implements HeapInterface { private T[] backingArray; private int size; // Do not add any more instance variables. Do not change the declaration  // of the instance variables above.   /**  * Creates a Heap with an initial capacity of {@code INITIAL_CAPACITY}  * for the backing array.  *  * Use the constant field in the interface. Do not use magic numbers!  */  public MaxHeap() { backingArray = (T[]) new Comparable[INITIAL_CAPACITY]; } 

 /** * Creates a properly ordered heap from a set of initial values.  *  * The initial array before the Build Heap algorithm takes place should  * contain the data in the same order as it appears in the ArrayList.  *  * The {@code backingArray} should have capacity 2n + 1 where n is the  * number of data in the passed in ArrayList (not INITIAL_CAPACITY from  * the interface). Index 0 should remain empty, indices 1 to n should  * contain the data in proper order, and the rest of the indices should  * be empty.  *  * @param data a list of data to initialize the heap with  * @throws IllegalArgumentException if data or any element in data is null  */  public buildHeap(ArrayList data) { if (data == null) { throw new IllegalArgumentException("Cannot insert null data into"  + " data structure."); } backingArray = (T[]) new Comparable[INITIAL_CAPACITY * 2 + 1];   int len = data.size(); for (int i = len / 2; i > 0; i--) { upHeap(); } for (int i = 0; i < data.size(); i++) { backingArray[i + 1] = data.get(i); } } 

...

I got this error messages

1.

Checking if MaxHeap(ArrayList throws IllegalArgumentException when data is null...

2.

Checking if HeapBuild works... (correct organization of heap) Initial: [ null 25 10 30 35 40 53 20 2 99 3 232 222 89 null null null null null null null null null null null null null ] Expected: [ null 232 99 222 35 40 89 20 2 25 3 10 53 30 null null null null null null null null null null null null null ] Actual: [ null 25 10 30 35 40 53 20 2 99 3 232 222 89 null null null null null null null null null null null null null null null null null null null ]

public interface HeapInterfaceextends Comparablesuper T>> { public static final int INITIAL_CAPACITY = 16; /**  * Adds an item to the heap. If the backing array is full and you're trying  * to add a new item, then double its capacity. The data passed in will not  * be in the heap. Therefore, there will be no duplicates.  *  * @throws IllegalArgumentException if the item is null  * @param item the item to be added to the heap  */  public void add(T item); /**  * Removes and returns the first item of the heap. Null out all elements not  * existing in the heap after this operation. Do not decrease the capacity  * of the backing array.  *  * @throws java.util.NoSuchElementException if the heap is empty  * @return the item removed  */  public T remove(); /**  * Returns if the heap is empty or not.  * @return a boolean representing if the heap is empty  */  public boolean isEmpty(); /**  * Returns the size of the heap.  * @return the size of the heap  */  public int size(); /**  * Clears the heap and returns array to starting capacity.  */  public void clear(); /**  * Used for grading purposes only.  *  * DO NOT USE OR EDIT THIS METHOD!  *  * @return the backing array  */  public Comparable[] getBackingArray(); }