Why can't I override my interface methods?
<p>Let's say I have an interface as follows.</p>

<pre><code>interface CardHolder : IEnumerable&lt;Card&gt;
{
    /// &lt;summary&gt; ...
    void PutCard(Card card);

    /// &lt;summary&gt; ...
    void PutCards(Card[] card);

    /// Some more methods...
}
</code></pre>

<p>I implement it as follows.</p>

<pre><code>public class ArrayCardHolder : CardHolder
{
    private Card[] _cards;
    private int _size = 0;

    public ArrayCardHolder(int capacity)
    {
        _cards = new Card[capacity];
    }

    public void PutCard(Card card)
    {
        if (IsFull())
            throw new Exception("This CardHolder is full. Capacity: " + Capacity());

        _cards[_size++] = card;
    }

    public void PutCards(Card[] cards)
    {
        if (_size + cards.Length &gt; _cards.Length)
            throw new Exception("Adding the Cards would exceed this CardHolder its capacity. Capacity: " + Capacity());

        for (int index = 0; index &lt; cards.Length; index++)
            _cards[_size++] = cards[index];
    }
    public IEnumerator&lt;Card&gt; GetEnumerator()
    {
        for (int index = 0; index &lt; _size; index++)
            yield return _cards[index];
    }

    System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
    {
        return this.GetEnumerator();
    }

    ///More methods.

}
</code></pre>

<p>Why can I not use the <code>override</code> keyword in my <code>ArrayCardHolder</code> 
(e.g. <code>public void override PutCard(Card card) { ///implementation }</code> to indicate that the method implements (i.e. overrides) the interface? In that case, the project will refuse to build.</p>

<p>Why does it work however when overriding <code>ToString()</code>? And why doesn't it work when implementing <code>CompareTo(T t)</code> from <code>IComparable&lt;T&gt;</code>?</p>

<p>What should I use instead? I'm worried that the documentation from the interface will not apply to my implementing methods. Such is the case in Java when the <code>@Override</code> annotation is used.</p>