The difference between #import, #include and @class in Objective C

If you are an Apple iPhone/ iPad/ Safari developer wondering whats the difference between the Objective C constructs #include, #import and @class, read on :

#import and #include

C has the #include preprocessor for including libraries. Objective C supports both #import and #include preprocessors. Apple's recommended way of loading headers in Objective C is to use #import. If you use #include, your header files would need header guards to check if a related header file is already included or not. The #import preprocessor automatically keeps track of headers that have been included and ignores if a header is imported more than once. GNU Objective C compiler supports #import however, it would emit a warning discouraging the use of #import as its strictly not "C" compatible. You can turn off the warning by using the -Wno-import option in the GNU Objective C compiler.

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If your code is strictly in Objective C and you are looking at strictly supporting Apple SDKs, use #import as the pre-processor. You can turn off the warning by using the -Wno-import option in the GNU Objective C compiler.


#import and @class

As discussed before, #import is a preprocessor that requires the compiler to include the header file. But what if, the class itself is not available to be included or there is a circular reference between class A and class B?

Thats when the construct @class is useful. @class is a "forward declaration" and whenever the compiler encounters an @class forward declaration, the compiler just notes that the actual declaration of the class is coming forward and hence doesnt worry about anything about that class, other than to reserve the memory allocation for a pointer whenever an instance of such forward declared classes are referred to.

For example, in the code

@class A
@interface B :NSObject {
A * instance;  
}

Here, since class A is a forward declaration, the compiler just reserves the memory for a pointer and ignores further validation.

Forward declaration not only reduces the pre-processing overheads and makes compilation & linking faster, but also helps better development as the implementation of class A can be "defered" without impacting the development of class B.

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In general use this as a rule of thumb, whenever you are in doubt about #import vs @class :

1. Always import the header files and framework classes by using #import.
2. Whenever you need to "send messages" to any class in your implementation, import the relevant headers using #import.
3. For all other scenarios, use forward declarations with @class.

Enabling Automatic Content ID Generation or Increment in Oracle UCM

The Content ID field needs to be specified manually while checking in content in Oracle Universal Content Management (UCM) Content Server, hitherto known as Stellent. The Content ID for any checked in document in the UCM Content Server needs to be unique and is one of the mandatory metadata required during checkin.

This Content ID can be generated automatically as a number or as a sequence with a fixed String literal as prefix.

Any of the following simple steps can be executed to achieve the same :

1. Through the GUI : Start the Content Server. This can be done either by running the Admin Service in Microsoft Windows or by running IdcAdmin.exe under /admin/bin. Then go to the Content Server Page in a bowser window; follow the navigation path - Administration > Admin Server > [ServerName] > General Configuration. In this form, select the checkbox "Automatically assign a content ID on check in" and enter the prefix text in the field "Auto Number Prefix". 
2. Through the System Properties: In Microsoft Windows, goto Start menu -> Oracle Content Server  -> [ServerName] ->Utilities -> System Properties. In the Options tab, enable the checkbox "Automatically assign a content ID on check in" and enter the prefix text in the field "Auto Number Prefix". 
3. Through the Config : In the config.cfg file under /server/bin; under the section General Option Variables. Add the following two entries -

         IsAutoNumber=true
         AutoNumberPrefix=[ContentIDPrefix]

Now, Restart the Content Server and login to the Content Server page and check in any document. Once the checkin is through; you can see that the Content ID. During checkin, there is still a provision to override with a different Content ID if the user wishes to; as the field would now be optional instead of a mandatory field.

Steps to alter the maximum number of simultaenous user logins in Oracle XE.

I found it rather strange that to increase the maximum number of connections; you need to increase the processes and not through the web GUI. The steps to alter the maximum number of processes in Oracle XE is similar to Oracle full edition.

Login to the SQL Command Line as sysdba.

SQL> show parameter processes
NAME TYPE VALUE
------------------------------------------------------------------------
processes integer *40*


Then increase the processes.

SQL > alter system set processes=100 scope=spfile.

Restart the database server; Check the processes parameter for confirmation.

This shall increase the number of connections.