Defensive copy of Calendar

Question

Been trying to find the best way to implement a method that makes a defensive copy of a Calendar object.

eg:

public void setDate(Calendar date) {
            


        

Answer 1

Just wrap your Calendar object into ThreadLocal. This will guarantee that each instance of Calendar is used only by one thread. Something like this:

public class ThreadLocalCalendar
{
    private final static ThreadLocal  CALENDAR =
        new ThreadLocal  ()
        {
            @Override
            protected Calendar initialValue()
            {
                GregorianCalendar calendar = new GregorianCalendar();

                // Configure calendar here.  Set time zone etc.

                return calendar;
            }
        };

    // Called from multiple threads in parallel
    public void foo ()
    {
        Calendar calendar = CALENDAR.get ();

        calendar.setTime (new Date ());
        // Use calendar here safely, because it belongs to current thread
    }
}