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, 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.

Since:

1.1

See Also:

• Serialized Form

Constructor Summary

Constructors

Constructor	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.

Method Summary

Modifier and Type	Method	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.

Methods declared in class Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Modifier and Type	Method	Description
protected Object	clone()	Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. May cause performance issues, deadlocks and hangs.
final Class<? extends Object>	getClass()	Answers the unique instance of java.lang.Class which represents the class of the receiver.
final void	notify()	Causes one thread which is waiting on the receiver to be made ready to run.
final void	notifyAll()	Causes all threads which are waiting on the receiver to be made ready to run.
final void	wait()	Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
final void	wait(long time)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
final void	wait(long time, int frac)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

Constructor Details

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 UIDs generated via the no-arg constructor.

Parameters:

num - number for well-known UID

Method Details

hashCode

public int hashCode()

Returns the hash code value for this UID.

Overrides:

hashCode in class Object

Returns:

the hash code value for this UID

See Also:

• Object.equals(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 class Object

Parameters:

obj - the object to compare this UID to

Returns:

true if the given object is equivalent to this one, and false otherwise

See Also:

• Object.hashCode()

toString

public String toString()

Returns a string representation of this UID.

Overrides:

toString in class Object

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 - the DataOutput instance to write this UID 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 - the DataInput instance to read UID from

Returns:

unmarshalled UID instance

Throws:

IOException - if an I/O error occurs while performing this operation