The concurrent package in core has stated the following (under the Notes
section of its URL
'All classes are released to the public domain and may be used for any
purpose whatsoever without permission or acknowledgment. Portions of the
CopyOnWriteArrayList and ConcurrentReaderHashMap classes are adapted
from Sun JDK source code. These are copyright of Sun Microsystems, Inc,
and are used with their kind permission,' (link is
And further down from that page it states:
'Do I need a license to use it? Can I get one? No!'
Is this okay?