<p>
  A chain of if/else if statements is evaluated from top to bottom. At most, only one branch of the chain will be executed: the first one with a condition that evaluates to true.
</p>
<p>
  Therefore, duplicating a condition in a sequence of if/else if statements automatically leads to dead code. Usually, is due to a copy/paste error. Obviously it could lead to unexpected behavior.
</p>

<h2>Noncompliant Code Sample</h2>
<pre>
if (param == 1)
  openWindow();
else if (param == 2)
  closeWindow();
else if (param == 1)  // For sure this is a bug
  moveWindowToTheBackground();
</pre>

<h2>Compliant Solution</h2>
<pre>
if (param == 1)
  openWindow();
else if (param == 2)
  closeWindow();
else if (param == 3)
  moveWindowToTheBackground();
</pre>