public UID() 
{
                           
        synchronized (lock) {
            if (!hostUniqueSet) {
                hostUnique = (new SecureRandom()).nextInt();
                hostUniqueSet = true;
            }
            unique = hostUnique;
            if (lastCount == Short.MAX_VALUE) {
                boolean interrupted = Thread.interrupted();
                boolean done = false;
                while (!done) {
                    long now = System.currentTimeMillis();
                    if (now < = lastTime) {
                        // wait for time to change
                        try {
                            Thread.currentThread().sleep(1);
                        } catch (InterruptedException e) {
                            interrupted = true;
                        }
                    } else {
                        lastTime = now;
                        lastCount = Short.MIN_VALUE;
                        done = true;
                    }
                }
                if (interrupted) {
                    Thread.currentThread().interrupt();
                }
            }
            time = lastTime;
            count = lastCount++;
        }
}

Generates a UID that is unique over time with respect to the host that it was generated on.

 public UID(short num) 
{
        unique = 0;
        time = 0;
        count = num;
}

Creates a "well-known" UID. There are 2¹⁶ possible such well-known ids.

A UID created via this constructor will not clash with any UIDs generated via the no-arg constructor.

Parameters:

num - number for well-known UID

 public boolean equals(Object obj) 
{
        if (obj instanceof UID) {
            UID uid = (UID) obj;
            return (unique == uid.unique &&
                    count == uid.count &&
                    time == uid.time);
        } else {
            return false;
        }
}

Compares the specified object with this UID for equality. This method returns true if and only if the specified object is a UID instance with the same unique, time, and count values as this one.

 public int hashCode() 
{
        return (int) time + (int) count;
}

Returns the hash code value for this UID.

 public static UID read(DataInput in) throws IOException 
{
        int unique = in.readInt();
        long time = in.readLong();
        short count = in.readShort();
        return new UID(unique, time, count);
}

Constructs and returns a new UID instance by unmarshalling a binary representation from an DataInput instance.

Specifically, this method first invokes the given stream's DataInput#readInt() method to read a unique value, then it invoke's the stream's DataInput#readLong() method to read a time value, then it invoke's the stream's DataInput#readShort() method to read a count value, and then it creates and returns a new UID instance that contains the unique, time, and count values that were read from the stream.

 public String toString() 
{
        return Integer.toString(unique,16) + ":" +
            Long.toString(time,16) + ":" +
            Integer.toString(count,16);
}

Returns a string representation of this UID.

 public  void write(DataOutput out) throws IOException 
{
        out.writeInt(unique);
        out.writeLong(time);
        out.writeShort(count);
}

Marshals a binary representation of this UID to a DataOutput instance.

Specifically, this method first invokes the given stream's DataOutput#writeInt(int) method with this UID's unique value, then it invokes the stream's DataOutput#writeLong(long) method with this UID's time value, and then it invokes the stream's DataOutput#writeShort(int) method with this UID's count value.