https://openjdk.java.net/ 
/*
 * Copyright (c) 2003, 2014, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.util;

import java.security.*;

import jdk.internal.misc.JavaLangAccess;
import jdk.internal.misc.SharedSecrets;


A class that represents an immutable universally unique identifier (UUID).
A UUID represents a 128-bit value.

 There exist different variants of these global identifiers.  The methods
of this class are for manipulating the Leach-Salz variant, although the
constructors allow the creation of any variant of UUID (described below).

 The layout of a variant 2 (Leach-Salz) UUID is as follows:
The most significant long consists of the following unsigned fields:

0xFFFFFFFF00000000 time_low
0x00000000FFFF0000 time_mid
0x000000000000F000 version
0x0000000000000FFF time_hi


The least significant long consists of the following unsigned fields:

0xC000000000000000 variant
0x3FFF000000000000 clock_seq
0x0000FFFFFFFFFFFF node



 The variant field contains a value which identifies the layout of the UUID. The bit layout described above is valid only for a 
UUID with a variant value of 2, which indicates the Leach-Salz variant. 
 The version field holds a value that describes the type of this 
UUID. There are four different basic types of UUIDs: time-based, DCE security, name-based, and randomly generated UUIDs. These types have a version value of 1, 2, 3 and 4, respectively. 
 For more information including algorithms used to create UUIDs, see  RFC 4122: A
Universally Unique IDentifier (UUID) URN Namespace, section 4.2
"Algorithms for Creating a Time-Based UUID".

Since:  1.5
/**
 * A class that represents an immutable universally unique identifier (UUID).
 * A UUID represents a 128-bit value.
 *
 * <p> There exist different variants of these global identifiers.  The methods
 * of this class are for manipulating the Leach-Salz variant, although the
 * constructors allow the creation of any variant of UUID (described below).
 *
 * <p> The layout of a variant 2 (Leach-Salz) UUID is as follows:
 *
 * The most significant long consists of the following unsigned fields:
 * <pre>
 * 0xFFFFFFFF00000000 time_low
 * 0x00000000FFFF0000 time_mid
 * 0x000000000000F000 version
 * 0x0000000000000FFF time_hi
 * </pre>
 * The least significant long consists of the following unsigned fields:
 * <pre>
 * 0xC000000000000000 variant
 * 0x3FFF000000000000 clock_seq
 * 0x0000FFFFFFFFFFFF node
 * </pre>
 *
 * <p> The variant field contains a value which identifies the layout of the
 * {@code UUID}.  The bit layout described above is valid only for a {@code
 * UUID} with a variant value of 2, which indicates the Leach-Salz variant.
 *
 * <p> The version field holds a value that describes the type of this {@code
 * UUID}.  There are four different basic types of UUIDs: time-based, DCE
 * security, name-based, and randomly generated UUIDs.  These types have a
 * version value of 1, 2, 3 and 4, respectively.
 *
 * <p> For more information including algorithms used to create {@code UUID}s,
 * see <a href="http://www.ietf.org/rfc/rfc4122.txt"> <i>RFC&nbsp;4122: A
 * Universally Unique IDentifier (UUID) URN Namespace</i></a>, section 4.2
 * &quot;Algorithms for Creating a Time-Based UUID&quot;.
 *
 * @since   1.5
 */
public final class UUID implements java.io.Serializable, Comparable<UUID> {

    
Explicit serialVersionUID for interoperability.

/**
     * Explicit serialVersionUID for interoperability.
     */
    private static final long serialVersionUID = -4856846361193249489L;

    /*
     * The most significant 64 bits of this UUID.
     *
     * @serial
     */
    private final long mostSigBits;

    /*
     * The least significant 64 bits of this UUID.
     *
     * @serial
     */
    private final long leastSigBits;

    private static final JavaLangAccess jla = SharedSecrets.getJavaLangAccess();

    /*
     * The random number generator used by this class to create random
     * based UUIDs. In a holder class to defer initialization until needed.
     */
    private static class Holder {
        static final SecureRandom numberGenerator = new SecureRandom();
    }

    // Constructors and Factories

    /*
     * Private constructor which uses a byte array to construct the new UUID.
     */
    private UUID(byte[] data) {
        long msb = 0;
        long lsb = 0;
        assert data.length == 16 : "data must be 16 bytes in length";
        for (int i=0; i<8; i++)
            msb = (msb << 8) | (data[i] & 0xff);
        for (int i=8; i<16; i++)
            lsb = (lsb << 8) | (data[i] & 0xff);
        this.mostSigBits = msb;
        this.leastSigBits = lsb;
    }

    
Constructs a new UUID using the specified data. 
mostSigBits is used for the most significant 64 bits of the 
UUID and leastSigBits becomes the least significant 64 bits of the UUID. 
Params:
  • mostSigBits –  The most significant bits of the UUID
  • leastSigBits –  The least significant bits of the UUID
/**
     * Constructs a new {@code UUID} using the specified data.  {@code
     * mostSigBits} is used for the most significant 64 bits of the {@code
     * UUID} and {@code leastSigBits} becomes the least significant 64 bits of
     * the {@code UUID}.
     *
     * @param  mostSigBits
     *         The most significant bits of the {@code UUID}
     *
     * @param  leastSigBits
     *         The least significant bits of the {@code UUID}
     */
    public UUID(long mostSigBits, long leastSigBits) {
        this.mostSigBits = mostSigBits;
        this.leastSigBits = leastSigBits;
    }

    
Static factory to retrieve a type 4 (pseudo randomly generated) UUID. The UUID is generated using a cryptographically strong pseudo random number generator. 
Returns: A randomly generated UUID
/**
     * Static factory to retrieve a type 4 (pseudo randomly generated) UUID.
     *
     * The {@code UUID} is generated using a cryptographically strong pseudo
     * random number generator.
     *
     * @return  A randomly generated {@code UUID}
     */
    public static UUID randomUUID() {
        SecureRandom ng = Holder.numberGenerator;

        byte[] randomBytes = new byte[16];
        ng.nextBytes(randomBytes);
        randomBytes[6]  &= 0x0f;  /* clear version        */
        randomBytes[6]  |= 0x40;  /* set to version 4     */
        randomBytes[8]  &= 0x3f;  /* clear variant        */
        randomBytes[8]  |= 0x80;  /* set to IETF variant  */
        return new UUID(randomBytes);
    }

    
Static factory to retrieve a type 3 (name based) UUID based on the specified byte array. 
Params:
  • name –  A byte array to be used to construct a UUID
Returns: A UUID generated from the specified array
/**
     * Static factory to retrieve a type 3 (name based) {@code UUID} based on
     * the specified byte array.
     *
     * @param  name
     *         A byte array to be used to construct a {@code UUID}
     *
     * @return  A {@code UUID} generated from the specified array
     */
    public static UUID nameUUIDFromBytes(byte[] name) {
        MessageDigest md;
        try {
            md = MessageDigest.getInstance("MD5");
        } catch (NoSuchAlgorithmException nsae) {
            throw new InternalError("MD5 not supported", nsae);
        }
        byte[] md5Bytes = md.digest(name);
        md5Bytes[6]  &= 0x0f;  /* clear version        */
        md5Bytes[6]  |= 0x30;  /* set to version 3     */
        md5Bytes[8]  &= 0x3f;  /* clear variant        */
        md5Bytes[8]  |= 0x80;  /* set to IETF variant  */
        return new UUID(md5Bytes);
    }

    
Creates a UUID from the string standard representation as described in the toString method. 
Params:
  • name –  A string that specifies a UUID
Throws:
Returns: A UUID with the specified value
/**
     * Creates a {@code UUID} from the string standard representation as
     * described in the {@link #toString} method.
     *
     * @param  name
     *         A string that specifies a {@code UUID}
     *
     * @return  A {@code UUID} with the specified value
     *
     * @throws  IllegalArgumentException
     *          If name does not conform to the string representation as
     *          described in {@link #toString}
     *
     */
    public static UUID fromString(String name) {
        int len = name.length();
        if (len > 36) {
            throw new IllegalArgumentException("UUID string too large");
        }

        int dash1 = name.indexOf('-', 0);
        int dash2 = name.indexOf('-', dash1 + 1);
        int dash3 = name.indexOf('-', dash2 + 1);
        int dash4 = name.indexOf('-', dash3 + 1);
        int dash5 = name.indexOf('-', dash4 + 1);

        // For any valid input, dash1 through dash4 will be positive and dash5
        // negative, but it's enough to check dash4 and dash5:
        // - if dash1 is -1, dash4 will be -1
        // - if dash1 is positive but dash2 is -1, dash4 will be -1
        // - if dash1 and dash2 is positive, dash3 will be -1, dash4 will be
        //   positive, but so will dash5
        if (dash4 < 0 || dash5 >= 0) {
            throw new IllegalArgumentException("Invalid UUID string: " + name);
        }

        long mostSigBits = Long.parseLong(name, 0, dash1, 16) & 0xffffffffL;
        mostSigBits <<= 16;
        mostSigBits |= Long.parseLong(name, dash1 + 1, dash2, 16) & 0xffffL;
        mostSigBits <<= 16;
        mostSigBits |= Long.parseLong(name, dash2 + 1, dash3, 16) & 0xffffL;
        long leastSigBits = Long.parseLong(name, dash3 + 1, dash4, 16) & 0xffffL;
        leastSigBits <<= 48;
        leastSigBits |= Long.parseLong(name, dash4 + 1, len, 16) & 0xffffffffffffL;

        return new UUID(mostSigBits, leastSigBits);
    }

    // Field Accessor Methods

    
Returns the least significant 64 bits of this UUID's 128 bit value.

Returns: The least significant 64 bits of this UUID's 128 bit value
/**
     * Returns the least significant 64 bits of this UUID's 128 bit value.
     *
     * @return  The least significant 64 bits of this UUID's 128 bit value
     */
    public long getLeastSignificantBits() {
        return leastSigBits;
    }

    
Returns the most significant 64 bits of this UUID's 128 bit value.

Returns: The most significant 64 bits of this UUID's 128 bit value
/**
     * Returns the most significant 64 bits of this UUID's 128 bit value.
     *
     * @return  The most significant 64 bits of this UUID's 128 bit value
     */
    public long getMostSignificantBits() {
        return mostSigBits;
    }

    
The version number associated with this UUID. The version number describes how this UUID was generated. The version number has the following meaning: 
    

  • 1    Time-based UUID

  • 2    DCE security UUID

  • 3    Name-based UUID

  • 4    Randomly generated UUID



Returns: The version number of this UUID
/**
     * The version number associated with this {@code UUID}.  The version
     * number describes how this {@code UUID} was generated.
     *
     * The version number has the following meaning:
     * <ul>
     * <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 {@code UUID}
     */
    public int version() {
        // Version is bits masked by 0x000000000000F000 in MS long
        return (int)((mostSigBits >> 12) & 0x0f);
    }

    
The variant number associated with this UUID. The variant number describes the layout of the UUID. The variant number has the following meaning: 
    

  • 0    Reserved for NCS backward compatibility

  • 2    IETF RFC 4122
(Leach-Salz), used by this class

  • 6    Reserved, Microsoft Corporation backward compatibility

  • 7    Reserved for future definition



Returns: The variant number of this UUID
/**
     * The variant number associated with this {@code UUID}.  The variant
     * number describes the layout of the {@code UUID}.
     *
     * The variant number has the following meaning:
     * <ul>
     * <li>0    Reserved for NCS backward compatibility
     * <li>2    <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF&nbsp;RFC&nbsp;4122</a>
     * (Leach-Salz), used by this class
     * <li>6    Reserved, Microsoft Corporation backward compatibility
     * <li>7    Reserved for future definition
     * </ul>
     *
     * @return  The variant number of this {@code UUID}
     */
    public int variant() {
        // This field is composed of a varying number of bits.
        // 0    -    -    Reserved for NCS backward compatibility
        // 1    0    -    The IETF aka Leach-Salz variant (used by this class)
        // 1    1    0    Reserved, Microsoft backward compatibility
        // 1    1    1    Reserved for future definition.
        return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
                      & (leastSigBits >> 63));
    }

    
The timestamp value associated with this UUID.

 The 60 bit timestamp value is constructed from the time_low, time_mid, and time_hi fields of this UUID. The resulting timestamp is measured in 100-nanosecond units since midnight, October 15, 1582 UTC. 
 The timestamp 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. 
Throws:
Returns:The timestamp of this UUID.
/**
     * 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 {@code UUID}.  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 {@code UUID} is not a time-based UUID then
     * this method throws UnsupportedOperationException.
     *
     * @throws UnsupportedOperationException
     *         If this UUID is not a version 1 UUID
     * @return The timestamp of this {@code UUID}.
     */
    public long timestamp() {
        if (version() != 1) {
            throw new UnsupportedOperationException("Not a time-based UUID");
        }

        return (mostSigBits & 0x0FFFL) << 48
             | ((mostSigBits >> 16) & 0x0FFFFL) << 32
             | mostSigBits >>> 32;
    }

    
The clock sequence value associated with this UUID.

 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.

 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. 
Throws:
Returns: The clock sequence of this UUID
/**
     * 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 {@code 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 {@code UUID}
     *
     * @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");
        }

        return (int)((leastSigBits & 0x3FFF000000000000L) >>> 48);
    }

    
The node value associated with this UUID.

 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.

 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.

Throws:
Returns: The node value of this UUID
/**
     * 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 {@code UUID}
     *
     * @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");
        }

        return leastSigBits & 0x0000FFFFFFFFFFFFL;
    }

    // Object Inherited Methods

    
Returns a String object representing this UUID. 
 The UUID string representation is as described by this BNF:


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"



Returns: A string representation of this UUID
/**
     * Returns a {@code String} object representing this {@code UUID}.
     *
     * <p> The UUID string representation is as described by this BNF:
     * <blockquote><pre>
     * {@code
     * 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></blockquote>
     *
     * @return  A string representation of this {@code UUID}
     */
    public String toString() {
        return jla.fastUUID(leastSigBits, mostSigBits);
    }

    
Returns a hash code for this UUID. 
Returns: A hash code value for this UUID
/**
     * Returns a hash code for this {@code UUID}.
     *
     * @return  A hash code value for this {@code UUID}
     */
    public int hashCode() {
        long hilo = mostSigBits ^ leastSigBits;
        return ((int)(hilo >> 32)) ^ (int) hilo;
    }

    
Compares this object to the specified object. The result is 
true if and only if the argument is not null, is a UUID object, has the same variant, and contains the same value, bit for bit, as this UUID. 
Params:
  • obj – 
        The object to be compared
Returns: true if the objects are the same; false otherwise
/**
     * Compares this object to the specified object.  The result is {@code
     * true} if and only if the argument is not {@code null}, is a {@code UUID}
     * object, has the same variant, and contains the same value, bit for bit,
     * as this {@code UUID}.
     *
     * @param  obj
     *         The object to be compared
     *
     * @return  {@code true} if the objects are the same; {@code false}
     *          otherwise
     */
    public boolean equals(Object obj) {
        if ((null == obj) || (obj.getClass() != UUID.class))
            return false;
        UUID id = (UUID)obj;
        return (mostSigBits == id.mostSigBits &&
                leastSigBits == id.leastSigBits);
    }

    // Comparison Operations

    
Compares this UUID with the specified UUID.

 The first of two UUIDs is greater than the second if the most
significant field in which the UUIDs differ is greater for the first
UUID.

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