- 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, anintthat uniquely identifies the VM that thisUIDwas generated in, with respect to its host and at the time represented by thetimevalue (an example implementation of theuniquevalue would be a process identifier), or zero for a well-knownUIDtime, alongequal to a time (as returned bySystem.currentTimeMillis()) at which the VM that thisUIDwas generated in was alive, or zero for a well-knownUIDcount, ashortto distinguishUIDs generated in the same VM with the sametimevalue
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:
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionbooleanCompares the specified object with thisUIDfor equality.inthashCode()Returns the hash code value for thisUID.static UIDConstructs and returns a newUIDinstance by unmarshalling a binary representation from anDataInputinstance.toString()Returns a string representation of thisUID.voidwrite(DataOutput out) Marshals a binary representation of thisUIDto aDataOutputinstance.
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Constructor Details
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UID
public UID()Generates aUIDthat 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
UIDcreated via this constructor will not clash with anyUIDs generated via the no-arg constructor.- Parameters:
num- number for well-knownUID
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Method Details
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hashCode
public int hashCode()Returns the hash code value for thisUID. -
equals
Compares the specified object with thisUIDfor equality. This method returnstrueif and only if the specified object is aUIDinstance with the sameunique,time, andcountvalues as this one. -
toString
Returns a string representation of thisUID. -
write
Marshals a binary representation of thisUIDto aDataOutputinstance.Specifically, this method first invokes the given stream's
DataOutput.writeInt(int)method with thisUID'suniquevalue, then it invokes the stream'sDataOutput.writeLong(long)method with thisUID'stimevalue, and then it invokes the stream'sDataOutput.writeShort(int)method with thisUID'scountvalue.- Parameters:
out- theDataOutputinstance to write thisUIDto- Throws:
IOException- if an I/O error occurs while performing this operation
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read
Constructs and returns a newUIDinstance by unmarshalling a binary representation from anDataInputinstance.Specifically, this method first invokes the given stream's
DataInput.readInt()method to read auniquevalue, then it invoke's the stream'sDataInput.readLong()method to read atimevalue, then it invoke's the stream'sDataInput.readShort()method to read acountvalue, and then it creates and returns a newUIDinstance that contains theunique,time, andcountvalues that were read from the stream.- Parameters:
in- theDataInputinstance to readUIDfrom- Returns:
- unmarshalled
UIDinstance - Throws:
IOException- if an I/O error occurs while performing this operation
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