When I tried to call a class in Java, an error occured
<p>When I tried to call a class called "ShowHistory" in Java, an error shows: "The type ShowHistory must implement the inherited abstract method ActionListener.actionPerformed(ActionEvent)"</p>

<p>Here is my code:</p>

<pre><code>    public class ShowHistory extends JFrame implements ActionListener {
   ...
    }
</code></pre>

<p>The IDE recommended me to make this class to be an abstract class, but when I convert it to be abstract, another piece of code goes wrong:</p>

<pre><code>            ShowHistory frame = new ShowHistory();
</code></pre>

<p>It shows: "Cannot instantiate the type ShowHistory".</p>

<p>Is there any idea to solve this problem?</p>
