实现Stack

public interface Stack<E> {
    void push(E e);
    E pop();
    E peek();
    int getSize();
    boolean isEmpty();
}

public class ArrayStack<E> implements Stack<E> {
	// 这里使用自己实现的ArrayList
  private ArrayList<E> array;
  public ArrayStack(int capacity){
    array = new ArrayList<>(capacity);
  }
  public ArrayStack(){
    array = new ArrayList<>();
  }
  @Override
  public void push(E e){
    array.addLast(e);
  }

  @Override
  public E pop() {
    return array.removeLast();
  }

  @Override
  public E peek() {
    return array.getLast();
  }

  @Override
  public int getSize() {
    return array.getSize();
  }

  @Override
  public boolean isEmpty() {
    return array.isEmpty();
  }

  public int getCapacity() {
    return array.getcapacity();
  }

  @Override
  public String toString() {
    StringBuilder res = new StringBuilder();
    res.append("Stack:");
    res.append('[');
    for (int i = 0; i < array.getSize() ; i++) {
      res.append(array.get(i));
      if (i != array.getSize() - 1){
        res.append(',');
      }
    }
    res.append("] top");
    return res.toString();
  }
}