import java.util.Arrays;
import java.util.Iterator;
public class AStack<T> implements IStack<T>
{
    private Object[] entries;
    private int top;
    public AStack()
    {
        entries = new Object[10];
        top = 0;
    }
    public void push(T newItem)
    {
        if(top >= entries.length)
        {
            resizeArray();
        }
        entries[top] = newItem;
        top++;
    }
    @SuppressWarnings("unchecked")
    public T peek()
    {
        if(isEmpty())
        {
            throw new EmptyStackException();
        }
        return (T)entries[top - 1];
    }
    @SuppressWarnings("unchecked")
    public T pop()
    {
        if(isEmpty())
        {
            throw new EmptyStackException();
        }
        T out = (T)entries[top - 1];
        entries[top - 1] = null;   //interest the garbage collector
        top--;
        return out;
    }
    public void clear()
    {
        for(int k = 0; k < top; k++)
        {
            entries[k] = null;
        }
        top = 0;
    }
    public boolean isEmpty()
    {
        return top == 0;
    }
    public int size()
    {
        return top;
    }
    public Iterator<T> iterator()
    {
        return new Navigator();
    }
    class Navigator implements Iterator<T>
    {
        private int nav;
        public Navigator()
        {
            nav = top;
        }
        public void remove()
        {
            throw new UnsupportedOperationException();
        }
        public boolean hasNext()
        {
            return nav > 0;
        }
        @SuppressWarnings("unchecked")
        public T next()
        {
            T out = (T)entries[nav - 1];
            nav--;
            return out;
        }
    }
    @Override
    public String toString()
    {
        if(isEmpty())
        {
              return "[]";
        }
        StringBuffer sb = new StringBuffer();
        sb.append("[");
        for(int k = top - 1; k > 0; k--)
        {
            sb.append(String.format("%s, ", entries[k]));
        }
        sb.append(String.format("%s]", entries[0]));
        return sb.toString();
    }
    private int newSize(int n)
    {
        return n < 1000? 2*n : 3*n/2;
    }
    private void resizeArray()
    {
        int n = entries.length;
        int newLength = newSize(n);
        entries = Arrays.copyOf(entries, newLength);

    }
    public static void main(String[] args)
    {
        /*IStack<String> s = new AStack<String>();
        s.push("A");
        s.push("B");
        s.push("C");
        System.out.println(s);
        System.out.println(s.size());
        s.pop();
        s.pop();
        s.pop();
        System.out.println(s);
        System.out.println(s.isEmpty());*/
        IStack<String> s = new AStack<>();
        for(int k = 0; k < 10; k++)
        {
            s.push("" + k);
        }
        System.out.println(s.size());
        System.out.println("********************");
        for(String k : s)
        {
            System.out.println(k);
        }
        for(int k = 0; k < 10; k++)
        {
            s.pop();
        }
        System.out.println(s.isEmpty());
        
    }
}