Method setMaxPriority of class ThreadGroup is not consistent in
its treatment of maximum priority relative to class Thread:

(a) If the argument is less than Thread.MIN_PRIORITY, it should
    signal an IllegalArgumentException, not quietly replace the
    argument with Thread.MIN_PRIORITY.
(b) Instead of requiring the maxPriority to decrease monotonically,
    it should allow the maxPriority to be set to any value not greater
    than the maxPriority of its parent.

I recommend the following new definition:

    public final synchronized void setMaxPriority(int newMaxPriority) {
	checkAccess();
	if (newMaxPriority < MIN_PRIORITY) {
	    throw new IllegalArgumentException();
	}
	int limit = (parent != null) ? parent.maxPriority : Thread.MAX_PRIORITY;
	if (newMaxPriority <= limit) {
	    maxPriority = newMaxPriority;
	}
	for (int i = 0 ; i < ngroups ; i++) {
	    groups[i].setMaxPriority(newMaxPriority);
	}
    }