Class UID
- java.lang.Object
-
- java.rmi.server.UID
- All Implemented Interfaces:
Serializable
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 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:
- Serialized Form
Constructor Summary
Constructor | Description |
---|---|
UID() | Generates a |
UID(short num) | Creates a "well-known" |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
boolean | equals(Object obj) | Compares the specified object with this |
int | hashCode() | Returns the hash code value for this |
static UID | read(DataInput in) | Constructs and returns a new |
String | toString() | Returns a string representation of this |
void | write(DataOutput out) | Marshals a binary representation of this |
Methods declared in class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
Constructor Detail
UID
public UID()
Generates a UID
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 any UID
s generated via the no-arg constructor.
- Parameters:
-
num
- number for well-knownUID
Method Detail
hashCode
public int hashCode()
Returns the hash code value for this UID
.
- Overrides:
-
hashCode
in classObject
- Returns:
- the hash code value for this
UID
- See Also:
-
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
equals
public boolean equals(Object obj)
Compares the specified object with this 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.
- Overrides:
-
equals
in classObject
- Parameters:
-
obj
- the object to compare thisUID
to - Returns:
-
true
if the given object is equivalent to this one, andfalse
otherwise - See Also:
-
Object.hashCode()
,HashMap
toString
public String toString()
Returns a string representation of this UID
.
write
public void write(DataOutput out) throws IOException
Marshals a binary representation of this 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.
- Parameters:
-
out
- theDataOutput
instance to write thisUID
to - Throws:
-
IOException
- if an I/O error occurs while performing this operation
read
public static UID read(DataInput in) throws IOException
Constructs and returns a new 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.
- Parameters:
-
in
- theDataInput
instance to readUID
from - Returns:
- unmarshalled
UID
instance - Throws:
-
IOException
- if an I/O error occurs while performing this operation