public final class UID extends Object implements Serializable
UID represents an identifier that is unique over time
with respect to the host it is generated on, or one of 216
"well-known" identifiers.
The UID() constructor can be used to generate an
identifier that is unique over time with respect to the host it is
generated on. The UID(short) constructor can be used to
create one of 216 well-known identifiers.
A UID instance contains three primitive values:
unique, an int that uniquely identifies
the VM that this UID was generated in, with respect to its
host and at the time represented by the time value (an
example implementation of the unique value would be a
process identifier),
or zero for a well-known UID
time, a long equal to a time (as returned
by System.currentTimeMillis()) at which the VM that this
UID was generated in was alive,
or zero for a well-known UID
count, a short to distinguish
UIDs generated in the same VM with the same
time value
An independently generated UID instance is unique
over time with respect to the host it is generated on as long as
the host requires more than one millisecond to reboot and its system
clock is never set backward. A globally unique identifier can be
constructed by pairing a UID instance with a unique host
identifier, such as an IP address.
| Constructor and Description |
|---|
UID()
Generates a
UID that is unique over time with
respect to the host that it was generated on. |
UID(short num)
Creates a "well-known"
UID. |
| Modifier and Type | Method and Description |
|---|---|
boolean |
equals(Object obj)
Compares the specified object with this
UID for
equality. |
int |
hashCode()
Returns the hash code value for this
UID. |
static UID |
read(DataInput in)
Constructs and returns a new
UID instance by
unmarshalling a binary representation from an
DataInput instance. |
String |
toString()
Returns a string representation of this
UID. |
void |
write(DataOutput out)
Marshals a binary representation of this
UID to
a DataOutput instance. |
public UID()
UID that is unique over time with
respect to the host that it was generated on.public UID(short num)
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.
num - number for well-known UIDpublic int hashCode()
UID.hashCode in class ObjectUIDObject.equals(java.lang.Object),
System.identityHashCode(java.lang.Object)public boolean equals(Object obj)
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.equals in class Objectobj - the object to compare this UID totrue if the given object is equivalent to
this one, and false otherwiseObject.hashCode(),
HashMappublic String toString()
UID.public void write(DataOutput out) throws IOException
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.
out - the DataOutput instance to write
this UID toIOException - if an I/O error occurs while performing
this operationpublic static UID read(DataInput in) throws IOException
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.
in - the DataInput instance to read
UID fromUID instanceIOException - if an I/O error occurs while performing
this operation Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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