CODEWITHSUNDEEP
javainstance-variables
user3766619
user3766619

Reputation: 63

Non-thread-safe fields should not be static, sonar lint error

hi i have this code sample with me.

 public class Util implements Serializable {


        private static final SimpleDateFormat DATE_KEY_FORMAT = new SimpleDateFormat("yyyyMMdd");
        private static final SimpleDateFormat EUS_WS_DATE_FORMAT = new SimpleDateFormat("yyyy-MM-dd");
        private static final SimpleDateFormat DATETIME_KEY_FORMAT = new SimpleDateFormat("yyyyMMddHHmmssSSS");
        public static final String TIME_ZONE_GMT = "GMT";


        /**
         * Returns date in the format yyyyMMdd
         * @return
         */
        public static int getyyyyMMdd() {
            return Integer.parseInt(DATE_KEY_FORMAT.format(new Date()));
        }

        public static int getyyyyMMdd(Date date) {
            return Integer.parseInt(DATE_KEY_FORMAT.format(date));
        }

        public static String getyyMMdd(Date dateTime) {
            return DATE_KEY_FORMAT.format(dateTime);
        }

        public static String getyyyyMMddHHmmssSSSCur(Date dateTime) {
            return DATETIME_KEY_FORMAT.format(dateTime);
        }

if i remove static from line : private static final SimpleDateFormat DATE_KEY_FORMAT = new SimpleDateFormat("yyyyMMdd"), then how to access it in non static manner? because it is showing error in below piece of code :

public static int getyyyyMMdd() {
        return Integer.parseInt(DATE_KEY_FORMAT.format(new Date()));
    }

can any body tell how to access it after removing the static? thanks in advance

Upvotes: 0

Views: 3704

Answers (3)

Fernando Ania
Fernando Ania

Reputation: 377

Static fields belong to the class whereas Instance variables belong to the object. Hence the value of a static field is shared across all instances of the class. Therefore if you attempt to call an instance variable from a static context it won't work, as the instance may not exist when the static method is called.

For example, for some class you call the util method getyyyMMdd() without instantiating the instance variable.

    public class SomeClass() {

       public SomeClass(){}

       public printDateInYears() {
           System.out.println(Util.getyyyyMMdd());
       }

    }

The only way to access an instance variable is to make the method getyyyyMMdd() not static.

Upvotes: 0

Andy Turner
Andy Turner

Reputation: 140484

Removing the static doesn't make it thread safe: instances can be accessed from separate threads concurrently.

Consider using a ThreadLocal<SimpleDateFormat>:

private static final ThreadLocal<SimpleDateFormat> DATE_KEY_FORMAT =
    ThreadLocal.withInitial(() -> new SimpleDateFormat("yyyyMMdd"));

and then access in the static methods like this:

return Integer.parseInt(DATE_KEY_FORMAT.get().format(new Date()));

Because each thread gets its own instance of SimpleDateFormat, there is no interference between the threads.

However, mutating changes to the SimpleDateFormat (e.g. setting the time zone) will be persisted in a given thread until you call DATE_KEY_FORMAT.remove(). But if you're never making changes to the instance like that, you don't need to worry about this.

Upvotes: 8

davidxxx
davidxxx

Reputation: 131436

An SimpleDateFormat instance is not thread safe and so should indeed not having concurrent access.
You should make the static methods instance methods as static methods cannot access instance members.
Note also that if the methods are accessed concurrently you would have the same concurrency issue. So in a multithreaded environment you should create the SimpleDateFormat instance inside each method (which may be expensive) or (less expensive) add the single instance of SimpleDateFormat in a ThreadLocal.

Upvotes: 1

Related Questions