Netbeans display running without actually opening Java application window
<p>I'm new to Java and is trying to run a Java awt/javax.swing application in Netbeans. Here is the <a href="https://github.com/dzjustinli2/Tetris" rel="nofollow noreferrer">github link</a>.</p>

<p>After I pressed run, nothing really happens even though Netbeans keeps displaying <code>running</code> in its window and a dot appeared under Java application icon (without actually opening a Java application window, I know this is the case because when I click the Java application icon with mouse, nothing happens).</p>

<p>What might be the cause of such problem?</p>

<p><a href="https://i.stack.imgur.com/1b0vi.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1b0vi.png" alt="enter image description here"></a></p>