Max heap in Java

I'm just looking for some feedback on my implementation of a maxheap mostly relating to style. I'm trying to create good habits as I learn to program.

Note: for the sort method I was given the precondition that the passed in array never has empty/null elements and that it must be sorted in place.

public class Heap12> implements PQueue{

  private E[] heap;                    // Backend data storage array
  private int size;                    // # elements in the heap

Private constructor that is used by the sort() method to heapify an array of objects type E. Size is initialized to 0 so that the objects in the array can be sorted in place by calling the add(E e) method.

@param E[] e - the array to be heapified

@SuppressWarnings("unchecked")
private Heap12(E[] e){
  this.heap = e;                     // Set heap array to passed in array
  this.size = 0;                     // Size HAS to be 0 initially
}

Public default no-arg constructor that initializes size to 0 and the backing array to a default capacity.

@SuppressWarnings("unchecked")
public Heap12(){
  this.size = 0;                     // Default values
  this.heap = (E[]) new Comparable[5];
}

Public copy constructor that takes in another Heap12 object. It creates
a new Heap12 object that is a deep copy of the passed in object. The underlying objects of the backing array are shared, but each Heap12 has its own instance variables.

@param Heap12 o - the Heap12 object to be copied

@SuppressWarnings("unchecked")
public Heap12(Heap12 o){
  this.heap = (E[]) new Comparable[o.heap.length];       
  this.size = o.size;                               // Copy size

  for(int i = 0; i < o.size(); i++){                // Copy each element
    this.heap[i] = o.heap[i];                       // reference
  }
}

Adds an element to this Heap12 object. Does not accept null elements, will throw a NullPointerException. If the Heap12 is at maximum capacity, the cap

One thing that I think need to be fixed is:

private Heap12(E[] e){
  this.heap = e;                     // Set heap array to passed in array
  this.size = 0;                     // Size HAS to be 0 initially
}

You need to copy it, otherwise the caller has reference to your array to corrupt it.

StackExchange Code Review Q#29089, answer score: 3