uuid.java

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     * <li>1    Time-based UUID
     * <li>2    DCE security UUID
     * <li>3    Name-based UUID
     * <li>4    Randomly generated UUID
     * </ul>
     *
     * @return  the version number of this <tt>UUID</tt>.
     */
    public int version() {
        if (version < 0) {
            // Version is bits masked by 0x000000000000F000 in MS long
            version = (int)((mostSigBits >> 12) & 0x0f);
        }
        return version;
    }

    /**
     * The variant number associated with this <tt>UUID</tt>. The variant 
     * number describes the layout of the <tt>UUID</tt>.
     *
     * The variant number has the following meaning:<p>
     * <ul>
     * <li>0    Reserved for NCS backward compatibility
     * <li>2    The Leach-Salz variant (used by this class)
     * <li>6    Reserved, Microsoft Corporation backward compatibility
     * <li>7    Reserved for future definition
     * </ul>
     *
     * @return  the variant number of this <tt>UUID</tt>.
     */
    public int variant() {
        if (variant < 0) {
            // This field is composed of a varying number of bits
            if ((leastSigBits >>> 63) == 0) {
                variant = 0;
            } else if ((leastSigBits >>> 62) == 2) {
                variant = 2;
            } else {
                variant = (int)(leastSigBits >>> 61);
            }
        }
        return variant;
    }

    /**
     * The timestamp value associated with this UUID.
     *
     * <p>The 60 bit timestamp value is constructed from the time_low,
     * time_mid, and time_hi fields of this <tt>UUID</tt>. The resulting 
     * timestamp is measured in 100-nanosecond units since midnight, 
     * October 15, 1582 UTC.<p>
     *
     * The timestamp value is only meaningful in a time-based UUID, which
     * has version type 1. If this <tt>UUID</tt> is not a time-based UUID then
     * this method throws UnsupportedOperationException.
     * 
     * @throws UnsupportedOperationException if this UUID is not a 
     *         version 1 UUID.
     */
    public long timestamp() {
        if (version() != 1) {
            throw new UnsupportedOperationException("Not a time-based UUID");
        }
        long result = timestamp;
        if (result < 0) {
            result = (mostSigBits & 0x0000000000000FFFL) << 48;
            result |= ((mostSigBits >> 16) & 0xFFFFL) << 32;
            result |= mostSigBits >>> 32;
            timestamp = result;
        }
        return result;
    }

    /**
     * The clock sequence value associated with this UUID.
     *
     * <p>The 14 bit clock sequence value is constructed from the clock
     * sequence field of this UUID. The clock sequence field is used to
     * guarantee temporal uniqueness in a time-based UUID.<p>
     *
     * The  clockSequence value is only meaningful in a time-based UUID, which
     * has version type 1. If this UUID is not a time-based UUID then
     * this method throws UnsupportedOperationException.
     * 
     * @return  the clock sequence of this <tt>UUID</tt>.
     * @throws UnsupportedOperationException if this UUID is not a 
     *         version 1 UUID.
     */
    public int clockSequence() {
        if (version() != 1) {
            throw new UnsupportedOperationException("Not a time-based UUID");
        }
        if (sequence < 0) {
            sequence = (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
        }
        return sequence;
    }

    /**
     * The node value associated with this UUID.
     *
     * <p>The 48 bit node value is constructed from the node field of
     * this UUID. This field is intended to hold the IEEE 802 address 
     * of the machine that generated this UUID to guarantee spatial
     * uniqueness.<p>
     *
     * The node value is only meaningful in a time-based UUID, which
     * has version type 1. If this UUID is not a time-based UUID then
     * this method throws UnsupportedOperationException.
     * 
     * @return  the node value of this <tt>UUID</tt>.
     * @throws UnsupportedOperationException if this UUID is not a
     *         version 1 UUID.
     */
    public long node() {
        if (version() != 1) {
            throw new UnsupportedOperationException("Not a time-based UUID");
        }
        if (node < 0) {
            node = leastSigBits & 0x0000FFFFFFFFFFFFL;
        }
        return node;
    }

    // Object Inherited Methods

    /**
     * Returns a <code>String</code> object representing this
     * <code>UUID</code>.
     * 
     * <p>The UUID string representation is as described by this BNF : 
     * <pre>
     *  UUID                   = <time_low> "-" <time_mid> "-"
     *                           <time_high_and_version> "-"
     *                           <variant_and_sequence> "-"
     *                           <node>
     *  time_low               = 4*<hexOctet>
     *  time_mid               = 2*<hexOctet>
     *  time_high_and_version  = 2*<hexOctet>
     *  variant_and_sequence   = 2*<hexOctet>
     *  node                   = 6*<hexOctet>
     *  hexOctet               = <hexDigit><hexDigit>
     *  hexDigit               =
     *        "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
     *        | "a" | "b" | "c" | "d" | "e" | "f"
     *        | "A" | "B" | "C" | "D" | "E" | "F"
     * </pre>
     *
     * @return  a string representation of this <tt>UUID</tt>.
     */
    public String toString() {
    return (digits(mostSigBits >> 32, 8) + "-" +
        digits(mostSigBits >> 16, 4) + "-" +
        digits(mostSigBits, 4) + "-" +
        digits(leastSigBits >> 48, 4) + "-" +
        digits(leastSigBits, 12));
    }

    /** Returns val represented by the specified number of hex digits. */
    private static String digits(long val, int digits) {
    long hi = 1L << (digits * 4);
    return Long.toHexString(hi | (val & (hi - 1))).substring(1);
    }

    /**
     * Returns a hash code for this <code>UUID</code>.
     *
     * @return  a hash code value for this <tt>UUID</tt>. 
     */
    public int hashCode() {
        if (hashCode == -1) {
            hashCode = (int)((mostSigBits >> 32) ^
                             mostSigBits ^
                             (leastSigBits >> 32) ^
                             leastSigBits);
        }
        return hashCode;
    }

    /**
     * Compares this object to the specified object.  The result is
     * <tt>true</tt> if and only if the argument is not
     * <tt>null</tt>, is a <tt>UUID</tt> object, has the same variant,
     * and contains the same value, bit for bit, as this <tt>UUID</tt>.
     *
     * @param   obj   the object to compare with.
     * @return  <code>true</code> if the objects are the same;
     *          <code>false</code> otherwise.
     */
    public boolean equals(Object obj) {
    if (!(obj instanceof UUID))
        return false;
        if (((UUID)obj).variant() != this.variant())
            return false;
        UUID id = (UUID)obj;
    return (mostSigBits == id.mostSigBits &&
                leastSigBits == id.leastSigBits);
    }

    // Comparison Operations

    /**
     * Compares this UUID with the specified UUID.
     * 
     * <p>The first of two UUIDs follows the second if the most significant
     * field in which the UUIDs differ is greater for the first UUID.
     *
     * @param  val <tt>UUID</tt> to which this <tt>UUID</tt> is to be compared.
     * @return -1, 0 or 1 as this <tt>UUID</tt> is less than, equal
     *         to, or greater than <tt>val</tt>.
     */
    public int compareTo(Object val) {
        UUID uuid = (UUID) val;
        // The ordering is intentionally set up so that the UUIDs
        // can simply be numerically compared as two numbers
        return (this.mostSigBits < uuid.mostSigBits ? -1 : 
                (this.mostSigBits > uuid.mostSigBits ? 1 :
                 (this.leastSigBits < uuid.leastSigBits ? -1 :
                  (this.leastSigBits > uuid.leastSigBits ? 1 :
                   0))));
    }

    /**
     * Reconstitute the <tt>UUID</tt> instance from a stream (that is,
     * deserialize it). This is necessary to set the transient fields
     * to their correct uninitialized value so they will be recomputed
     * on demand.
     */
    private void readObject(java.io.ObjectInputStream in)
        throws java.io.IOException, ClassNotFoundException {

        in.defaultReadObject();

        // Set "cached computation" fields to their initial values
        version = -1;
        variant = -1;
        timestamp = -1;
        sequence = -1;
        node = -1;
        hashCode = -1;
    }
}