抽象类和虚方法问题:无法将变量‘list’声明为抽象类型‘aStack<int>’aStack<int> list(5)

abstract class aStack<T>
{
    public abstract void Push(T item);
    public abstract T Pop();
}

class MyStack<T> : aStack<T>
{
    private List<T> stack;

    public MyStack(int capacity)
    {
        stack = new List<T>(capacity);
    }

    public override void Push(T item)
    {
        stack.Add(item);
    }

    public override T Pop()
    {
        if (stack.Count > 0)
        {
            T item = stack[stack.Count - 1];
            stack.RemoveAt(stack.Count - 1);
            return item;
        }
        else
        {
            throw new InvalidOperationException("Stack is empty.");
        }
    }
}

// 使用示例
MyStack<int> stack = new MyStack<int>(5);
stack.Push(1);
stack.Push(2);
int item = stack.Pop();
Console.WriteLine(item);  // 输出：2