Pattern: Static Calendar field
Issue: -
Calendar objects should not be used as static fields. Calendars are inherently unsafe for multi-threaded use. Sharing a single instance across thread boundaries without proper synchronization will result in erratic behavior of the application.
Under 1.4 problems seem to surface less often than under Java 5 where you will probably see random ArrayIndexOutOfBoundsException or IndexOutOfBoundsException in sun.util.calendar.BaseCalendar.getCalendarDateFromFixedDate(). You may also experience serialization problems. Using an instance field or a ThreadLocal is recommended.
Examples:
// Violations
class SomeClass {
static Calendar calendar1
static java.util.Calendar calendar2
static final CAL1 = Calendar.getInstance()
static final CAL2 = Calendar.getInstance(Locale.FRANCE)
static def cal3 = Calendar.getInstance(timezone)
static Object cal4 = Calendar.getInstance(timezone, locale)
}
// These usages are OK
class SomeCorrectClass {
private final Calendar calendar1
static ThreadLocal<Calendar> calendar2
}