<p>When either the equality operator in a null test or the logical operator that follows it is reversed, the code has the appearance of safely null-testing the object before dereferencing it. Unfortunately the effect is just the opposite - the object is null-tested and then dereferenced _only_ if it is null, leading to a guaranteed null pointer dereference.</p>

<h2>Noncompliant Code Sample</h2>
<pre>
if (str == null && str.length() == 0) {
  System.out.println("String is empty");
}

if (str != null || str.length() > 0) {
 System.out.println("String is not empty");
}
</pre>

<h2>Compliant Solution</h2>
<pre>
if (str == null || str.length() == 0) {
  System.out.println("String is empty");
}

if (str != null && str.length() > 0) {
  System.out.println("String is not empty");
}
</pre>