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public final class UID extends Object implements Serializable
A 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 {@link #UID()} constructor can be used to generate an identifier that is unique over time with respect to the host it is generated on. The {@link #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 {@link 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
UID
s 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 Summary | |
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UID() Generates a UID that is unique over time with
respect to the host that it was generated on.
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UID(short num) Creates a "well-known" UID .
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Method Summary | |
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boolean |
Compares the specified object with this UID for
equality.
|
int |
hashCode() Returns the hash code value for this UID .
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static UID |
Constructs and returns a new UID instance by
unmarshalling a binary representation from an
DataInput instance.
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String |
toString() Returns a string representation of this UID .
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void |
write(DataOutput out) Marshals a binary representation of this UID to
a DataOutput instance.
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Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
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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 UID
s generated via the no-arg
constructor.
num
- number for well-known UID
Method Detail |
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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 Object
obj
- the object to compare this UID
totrue
if the given object is equivalent to
this one, and false
otherwisepublic int hashCode()
UID
.
hashCode
in class Object
UID
public 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
{@link DataInput#readInt()} method to read a unique
value,
then it invoke's the stream's
{@link DataInput#readLong()} method to read a time
value,
then it invoke's the stream's
{@link 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 operationpublic String toString()
UID
.
toString
in class Object
UID
public void write(DataOutput out) throws IOException
UID
to
a DataOutput
instance.
Specifically, this method first invokes the given stream's
{@link DataOutput#writeInt(int)} method with this UID
's
unique
value, then it invokes the stream's
{@link DataOutput#writeLong(long)} method with this UID
's
time
value, and then it invokes the stream's
{@link 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 operation
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