Implement Stack using Arrays and LinkedList

Implement Stack using Arrays and LinkedList
public class MyStackArray<E> {
  private int size = 0;
  private static final int DEFAULT_CAPACITY = 10;
  private Object elements[];

  public MyStackArray() {
    elements = new Object[DEFAULT_CAPACITY];
  }

  public void push(E e) {
    if (size == elements.length) {
      ensureCapa();
    }
    elements[size++] = e;
  }

  @SuppressWarnings("unchecked")
  public E pop() {
    E e = (E) elements[--size];
    elements[size] = null;
    return e;
  }

  private void ensureCapa() {
    int newSize = elements.length * 2;
    elements = Arrays.copyOf(elements, newSize);
  }
}

// Use LinkedList
import java.util.ArrayList;

public class MyStackList<E> extends ArrayList<E> {

  private static final long serialVersionUID = 1L;

  public E pop() {
    E e = get(size() - 1);
    remove(size() - 1);
    return e;
  }

  public void push(E e) {
    add(e);
  }

}
https://gist.github.com/gcrfelix/736c75c6eee0372c6efc
从空间角度来看，如果存10000个元素，LinkedList和ArrayList哪个更节约空间？
答：ArrayList. 每存一个元素，LinkedList都需要占用一个指针和该元素的空间，所以他的空间一直是2n的占有量，但是ArrayList的长度是1,2,4,8....
增长，只有当element占满了array的长度arraylist才会扩容，所以他的空间占有量是<=2n。


import java.util.Arrays;

public class MyList<E> {
  private int size = 0;
  private static final int DEFAULT_CAPACITY = 10;
  private Object elements[];
 
  public MyList() {
    elements = new Object[DEFAULT_CAPACITY];
  }

  public void add(E e) {
    if (size == elements.length) {
      ensureCapa();
    }
    elements[size++] = e;
  }


  private void ensureCapa() {
    int newSize = elements.length * 2;
    elements = Arrays.copyOf(elements, newSize);
  }

  @SuppressWarnings("unchecked")
  public E get(int i) {
    if (i>= size || i <0) {
      throw new IndexOutOfBoundsException("Index: " + i + ", Size " + i);
    }
    return (E) elements[i];
  }
}