<p>Strings are immutable objects in Java, so concatenation doesn't simply add the new String to the end of the existing string. Instead, in each loop iteration, the first String is converted to an intermediate object type, the second string is appended, and then the intermediate object is converted back to a String. Further, performance of these intermediate operations degrades as the String gets longer. Therefore, the use of StringBuilder is preferred.</p>

<h2>Noncompliant Code Example</h2>
<pre>
String str = "";
for (int i = 0; i < arrayOfStrings.length ; ++i) {
  str = str + arrayOfStrings[i];
}
</pre>

<h2>Compliant Solution</h2>
<pre>
StringBuilder bld = new StringBuilder();
for (int i = 0; i < arrayOfStrings.length; ++i) {
  bld.append(arrayOfStrings[i]);
}
String str = bld.toString();
</pre>