Not all classes in the standard Java library were written to be thread-safe. Using them in a multi-threaded manner is highly likely to cause data problems or exceptions at runtime.


This rule raises an issue when an instance of ``++Calendar++``, ``++DateFormat++``, ``++javax.xml.xpath.XPath++``, or ``++javax.xml.validation.SchemaFactory++`` is marked ``++static++``.


== Noncompliant Code Example

----
public class MyClass {
  private static SimpleDateFormat format = new SimpleDateFormat("HH-mm-ss");  // Noncompliant
  private static Calendar calendar = Calendar.getInstance();  // Noncompliant
----


== Compliant Solution

----
public class MyClass {
  private SimpleDateFormat format = new SimpleDateFormat("HH-mm-ss");
  private Calendar calendar = Calendar.getInstance();
----