org.apache.derby.iapi.store.access
Interface DatabaseInstant

All Superinterfaces:
java.io.Serializable
All Known Subinterfaces:
LogInstant
All Known Implementing Classes:
LogCounter

public interface DatabaseInstant
extends java.io.Serializable

A DatabaseInstant is a quantity which the database associates with events to collate them. This interface is used in the column SYS.SYSSYNCINSTANTS.INSTANT.

Assume a database associates a DatabaseInstant to an event E1. We call this I(E1). Also assume the same Database associates a DatabaseInstant to a second event E2. We call this I(E2). By definition

  1. If I(E1) < I(E2) event E1 occurred before event E2
  2. If I(E2) = I(E2) event E1 is the same event as E2
  3. If I(E1) > I(E2) event E1 occurred after event E2

It is not meaningful to compare a DatabaseInstant from one database with a DatabaseInstant from another. The result of such a comparison is undefined. Because a database may construct, store and compare huge numbers of DatabaseInstants, this interface does not require an implementation to notice when a caller compares a DatabaseInstants from different databases.

Any implementation of this interface must implement value equality, thus implementing equals() and hashCode() methods.


Method Summary
 boolean equals(java.lang.Object other)
          Return true if this DatabaseInstant equals DatabaseInstant from the same database.
 boolean lessThan(DatabaseInstant other)
          Return true if this DatabaseInstant is before another DatabaseInstant from the same database.
 DatabaseInstant next()
          Return the next higher DatabaseInstant.
 DatabaseInstant prior()
          Return the next lower DatabaseInstant.
 java.lang.String toString()
          Convert the database instant to a string.
 

Method Detail

lessThan

boolean lessThan(DatabaseInstant other)
Return true if this DatabaseInstant is before another DatabaseInstant from the same database.

Parameters:
other - a DatabaseInstant from the same database as this.
Returns:
the comparison result. If 'other' is from another database the result is undefined.

equals

boolean equals(java.lang.Object other)
Return true if this DatabaseInstant equals DatabaseInstant from the same database.

Overrides:
equals in class java.lang.Object
Parameters:
other - a DatabaseInstant from the same database as this.
Returns:
the comparison result. If 'other' is from another database the result is undefined.

next

DatabaseInstant next()
Return the next higher DatabaseInstant. There is no requirement that a transaction with the next instant exist in the database. It is required that this.lessThan( this.next()), and that no instant can be between this and this.next(). If the DatabaseInstant is implemented using a integer then next() should return a new DatabaseInstant formed by adding one to the integer.

Returns:
the next possible DatabaseInstant

prior

DatabaseInstant prior()
Return the next lower DatabaseInstant. There is no requirement that a transaction with the next instant exist in the database. It is required that this.prior().lessThan( this), and that no instant can be between this and this.prior(). If the DatabaseInstant is implemented using a integer then prior() should return a new DatabaseInstant formed by subtracting one from the integer.

Returns:
the prior possible DatabaseInstant

toString

java.lang.String toString()
Convert the database instant to a string. This is mainly used for debugging.

Overrides:
toString in class java.lang.Object
Returns:
a string representation of the instant.

Built on Thu 2011-03-10 11:54:14+0000, from revision ???

Apache Derby V10.6 Internals - Copyright © 2004,2007 The Apache Software Foundation. All Rights Reserved.