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;
}
}
