fields with final keywords can be reassigned..?

Hi folks,
I have a question regarding the final modifier.

We all know the System class has the out, err, in static & final objects defined.

We can get the (out, err, in) Stream objects redirected any other using the System.setOut(), setErr() and setIn method and I could see the objects are getting changed once we do invoke these System.setXXX()methods.
Is it contradictory to what we have seen with the key word final.
I could see the Native implementations for the System.setXXX methods, in the JAVA src code.

Can anyone put some light on this.

Looking forward to see your valuable comments.

Regards,
kk