In a multi-threaded situation, un-``++synchronized++`` lazy initialization of static fields could mean that a second thread has access to a half-initialized object while the first thread is still creating it. Allowing such access could cause serious bugs. Instead. the initialization block should be ``++synchronized++``.


Similarly, updates of such fields should also be ``++synchronized++``.


This rule raises an issue whenever a lazy static initialization is done on a class with at least one ``++synchronized++`` method, indicating intended usage in multi-threaded applications.


== Noncompliant Code Example

----
private static Properties fPreferences = null;

private static Properties getPreferences() {
        if (fPreferences == null) {
            fPreferences = new Properties(); // Noncompliant
            fPreferences.put("loading", "true");
            fPreferences.put("filterstack", "true");
            readPreferences();
        }
        return fPreferences;
    }
}
----


== Compliant Solution

----
private static Properties fPreferences = null;

private static synchronized Properties getPreferences() {
        if (fPreferences == null) {
            fPreferences = new Properties();
            fPreferences.put("loading", "true");
            fPreferences.put("filterstack", "true");
            readPreferences();
        }
        return fPreferences;
    }
}
----

