The code example "SerialNum" in the class comment for ThreadLocal
can be better written using modern Java idioms:

class SerialNum {
    private static ThreadLocal<Integer> serialNum
	= new ThreadLocal<Integer>()
    {
	// The next serial number to be assigned
	private int nextSerialNum = 0;

	protected synchronized Integer initialValue() {
            return nextSerialNum++;
        }
    };

    public static int get() {
        return serialNum.get();
    }
}