- All Implemented Interfaces:
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
, anint
that uniquely identifies the VM that thisUID
was generated in, with respect to its host and at the time represented by thetime
value (an example implementation of theunique
value would be a process identifier), or zero for a well-knownUID
time
, along
equal to a time (as returned bySystem.currentTimeMillis()
) at which the VM that thisUID
was generated in was alive, or zero for a well-knownUID
count
, ashort
to distinguishUID
s generated in the same VM with the sametime
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.
- Since:
- 1.1
- See Also:
-
Constructor Summary
-
Method Summary
Modifier and TypeMethodDescriptionboolean
Compares the specified object with thisUID
for equality.int
hashCode()
Returns the hash code value for thisUID
.static UID
Constructs and returns a newUID
instance by unmarshalling a binary representation from anDataInput
instance.toString()
Returns a string representation of thisUID
.void
write
(DataOutput out) Marshals a binary representation of thisUID
to aDataOutput
instance.
-
Constructor Details
-
UID
public UID()Generates aUID
that is unique over time with respect to the host that it was generated on. -
UID
public UID(short num) Creates a "well-known"UID
. There are 216 possible such well-known ids.A
UID
created via this constructor will not clash with anyUID
s generated via the no-arg constructor.- Parameters:
num
- number for well-knownUID
-
-
Method Details
-
hashCode
-
equals
Compares the specified object with thisUID
for equality. This method returnstrue
if and only if the specified object is aUID
instance with the sameunique
,time
, andcount
values as this one. -
toString
-
write
Marshals a binary representation of thisUID
to aDataOutput
instance.Specifically, this method first invokes the given stream's
DataOutput.writeInt(int)
method with thisUID
'sunique
value, then it invokes the stream'sDataOutput.writeLong(long)
method with thisUID
'stime
value, and then it invokes the stream'sDataOutput.writeShort(int)
method with thisUID
'scount
value.- Parameters:
out
- theDataOutput
instance to write thisUID
to- Throws:
IOException
- if an I/O error occurs while performing this operation
-
read
Constructs and returns a newUID
instance by unmarshalling a binary representation from anDataInput
instance.Specifically, this method first invokes the given stream's
DataInput.readInt()
method to read aunique
value, then it invoke's the stream'sDataInput.readLong()
method to read atime
value, then it invoke's the stream'sDataInput.readShort()
method to read acount
value, and then it creates and returns a newUID
instance that contains theunique
,time
, andcount
values that were read from the stream.- Parameters:
in
- theDataInput
instance to readUID
from- Returns:
- unmarshalled
UID
instance - Throws:
IOException
- if an I/O error occurs while performing this operation
-