Java: many ways of casting a (long) Object to double

I have an Object obj that I know is actually a long. In some Math code I need it as double.

Is it safe to directly cast it to double?

double x = (double)obj;

Or should I rather cast it first to long and then to double.

double x = (double)(long)obj;

I also found another (less readable) alternative:

double x = new Long((long)obj).doubleValue();

What are the dangers/implications of doing either?

Solution Summary:

• obj is a Number and not a long.
• Java 6 requires explicit casting, e.g.: double x = ((Number)obj).doubleValue()
• Java 7 has working cast magic: double x = (long)obj

For more details on the Java6/7 issue also read discussion of TJ's answer.

Edit: I did some quick tests. Both ways of casting (explicit/magic) have the same performance.