new SimpleDateFormat always returns same reference for a given dateFormat

Question

I was trying to replicate a bug by using the same instance of SimpleDateFormat across multiple threads. However I got stuck with another problem and did not find any

Answer 1

SimpleDateFormat actually implements hashCode by returning the hashcode of the pattern.

You can verify that there are actually distinct objects by using System.identityHashCode():

System.out.println("d1 = " + d1 + " / " + System.identityHashCode(d1));
System.out.println("d2 = " + d2 + " / " + System.identityHashCode(d2));
System.out.println("d3 = " + d3 + " / " + System.identityHashCode(d3));

This will print 3 different values.