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 * {@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. * *
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. * *
For more information including algorithms used to create {@code UUID}s,
* see RFC 4122: A
* Universally Unique IDentifier (UUID) URN Namespace, section 4.2
* "Algorithms for Creating a Time-Based UUID".
*
* @since 1.5
*/
public final class UUID implements java.io.Serializable, Comparable 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.
*
* 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 {@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.
*
* @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 {@code String} object representing this {@code UUID}.
*
* The UUID string representation is as described by this BNF:
* 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))));
}
}
*
*
* @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 {@code UUID}. The variant
* number describes the layout of the {@code UUID}.
*
* The variant number has the following meaning:
*
*
*
* @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.
*
*
*
* @return A string representation of this {@code UUID}
*/
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}.
*
* @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 {@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.
*
*
* {@code
* UUID =