OpenJDK 27 · java.rmi.server.UID · APIdia, the JavaDoc alternative

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.

Field Summary

Modifier and Type	Field and Description
private final short	count 16-bit number to distinguish `UID` instances created in the same VM with the same time value
private static int	hostUnique
private static boolean	hostUniqueSet
private static short	lastCount
private static long	lastTime
private static final Object	lock
private static final long	serialVersionUID indicate compatibility with JDK 1.1.x version of class
private final long	time a time (as returned by `System#currentTimeMillis()`) at which the VM that this `UID` was generated in was alive
private final int	unique number that uniquely identifies the VM that this `UID` was generated in with respect to its host and at the given time

Constructor Summary

Access	Constructor and Description
public	UID() Generates a `UID` that is unique over time with respect to the host that it was generated on.
public	UID(short number for well-known `UID` num) Creates a "well-known" `UID`.
private	UID(int unique, long time, short count) Constructs a `UID` given data read from a stream.

Method Summary

Modifier and Type	Method and Description
public boolean	Returns: `true` if the given object is equivalent to this one, and `false` otherwise equals(Object the object to compare this `UID` to obj) Overrides java.lang.Object.equals. Compares the specified object with this `UID` for equality.
public int	Returns: the hash code value for this `UID` hashCode() Overrides java.lang.Object.hashCode. Returns the hash code value for this `UID`.
public static UID	Returns: unmarshalled `UID` instance read(DataInput the `DataInput` instance to read `UID` from in) Constructs and returns a new `UID` instance by unmarshalling a binary representation from an `DataInput` instance.
public String	Returns: a string representation of this `UID` toString() Overrides java.lang.Object.toString. Returns a string representation of this `UID`.
public void	write(DataOutput the `DataOutput` instance to write this `UID` to out) Marshals a binary representation of this `UID` to a `DataOutput` instance.

Inherited from java.lang.Object:: clone finalize getClass notify notifyAll wait wait wait

Field Detail

count	back to summary
private final short count 16-bit number to distinguish `UID` instances created in the same VM with the same time value

hostUnique	back to summary
private static int hostUnique

hostUniqueSet	back to summary
private static boolean hostUniqueSet

lastCount	back to summary
private static short lastCount

lastTime	back to summary
private static long lastTime

lock	back to summary
private static final Object lock

serialVersionUID	back to summary
private static final long serialVersionUID indicate compatibility with JDK 1.1.x version of class

time	back to summary
private final long time a time (as returned by `System#currentTimeMillis()`) at which the VM that this `UID` was generated in was alive

unique	back to summary
private final int unique number that uniquely identifies the VM that this `UID` was generated in with respect to its host and at the given time

Constructor Detail

UID	back to summary
public UID() Generates a `UID` that is unique over time with respect to the host that it was generated on.

UID back to summary

UID	back to summary
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:short number for well-known `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:short: number for well-known UID

UID	back to summary
private UID(int unique, long time, short count) Constructs a `UID` given data read from a stream.

Method Detail

equals back to summary

equals	back to summary
public boolean equals(Object obj) Overrides java.lang.Object.equals. 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. Parameters obj:Object the object to compare this `UID` to Returns:boolean `true` if the given object is equivalent to this one, and `false` otherwise

public boolean equals(Object obj)

Overrides java.lang.Object.equals.

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.

Parameters

obj:Object: the object to compare this UID to

Returns:boolean

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

hashCode back to summary

hashCode	back to summary
public int hashCode() Overrides java.lang.Object.hashCode. Returns the hash code value for this `UID`. Returns:int the hash code value for this `UID`

public int hashCode()

Overrides java.lang.Object.hashCode.

Returns the hash code value for this UID.

Returns:int: the hash code value for this UID

read back to summary

read	back to summary
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:DataInput the `DataInput` instance to read `UID` from Returns:UID unmarshalled `UID` instance Exceptions IOException: if an I/O error occurs while performing this operation

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:DataInput: the DataInput instance to read UID from

Returns:UID

unmarshalled UID instance

Exceptions

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

toString back to summary

toString	back to summary
public String toString() Overrides java.lang.Object.toString. Returns a string representation of this `UID`. Returns:String a string representation of this `UID`

public String toString()

Overrides java.lang.Object.toString.

Returns a string representation of this UID.

Returns:String: a string representation of this UID

write back to summary

write	back to summary
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:DataOutput the `DataOutput` instance to write this `UID` to Exceptions IOException: if an I/O error occurs while performing this operation

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:DataOutput: the DataOutput instance to write this UID to

Exceptions

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

public final Class UID

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail