Is it advisable to use inheritance when reusing dialogs/frames?

Hi!
While working on a project, I've noticed that there are instances when I could reuse code by creating general forms (as dialogs or windows) and subclassing them. For example, I have this set of dialogs which have a similar function: each dialog has a table (or list) of objects and functions for adding, deleting and editing objects in this table. Do you think that it's good to use inheritance in this case? That is, I create a general AddEditDeleteDialog from which to subclass particular dialogs, AddEditDeleteObject1Dialog, AddEditDeleteObject2Dialog, ...
Thanks!

Yes, of course. But to what extent? Should I include
layouting code, component initialization, event
handling, etc in the superclass (AddEditDeleteDialog),
or should I let the subclasses (AddEditDeleteObject1Dialog)
handle that?Basically, whatever is the same in all the subclasses can be placed in the superclass. If there are differences, then you should place it in the subclasses.
Things like event handling can be placed in the superclass, where each method in the event listener fires an abstract method in the superclass, which each of your subclasses implement to provide custom event handling.
Component initialization can also be used in the superclass for whatever components are used in all of the subclasses. Subclasses can then add any components which are unique to them.
You should also be aware that the purpose of inheritance is to add to the functionality of a class. If your subclass provides no extra abstract functionality then you should just use one class, and change some settings each time you need to use it for a different purpose. E.g. If your dialogs contain the same components, same actions etc but different text, then use just one class, and for each dialog, set the text for each of the components accordingly.
There is no hard/fast rule for using inheritance and how to design an object hierarchy, and as my first programming teacher used to say "every programming problem can usually be solved in loads of different ways."

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Why to use inheritance when import is sufficient

The import directive tells the compiler where to look for the class definitions when it comes upon a class that it cannot find in the default java.lang package. After an import statement has been included in our program we can use the methods related to that class as required and we are not required to give the fully qualified names.
In inheritance we extend a base class into a derived class so that the features and methods of the base class are available in the derived class which facilitates reusability. As per my understanding the same thing is facilitated by import statements. If it is so, why are we using inheritance if it can be done with the use of import statements?

Import statements and inheritance are completely different things.
Import statements tell the compiler how to expand brief class names into fully-qualified class names. It has nothing to do with the functionality of the code.
Inheritance changes the identification and functionality of the classes, and thus the functionality of the code.
Maybe you're really thinking about composition/delegation vs. inheritance. Composition is when a class has another class as a part of it, and delegation is when the class sends some of its work to the other class. You can have an object-oriented system without inheritance of implementations, using composition instead.

When to use inheritance and When to use Composition

java support both inheratiance and composition .I also know "is a" and
"has a realitionship" but there is always a problem with me to understanding whethere i have to use extends or having a object of a class has a member of othere class.
and also "A pure OOP must support polimorphisim,inheretiance,encapluction,Abstraction and Composition" correct me if i am wrong
thank you and have a nice day.

Bruce Eckel, author of Thinking In Java, has this to say about composition vs. inheritance:
When deciding between inheritance and composition, ask if you need to upcast to the base type. If not, prefer composition (member objects) to inheritance. This can eliminate the perceived need for multiple base types. If you inherit, users will think they are supposed to upcast.
Choose composition first when creating new classes from existing classes. You should only used inheritance if it is required by your design. If you use inheritance where composition will work, your designs will become needlessly complicated.
Bill Venners: Composition versus Inheritance
Use inheritance (of implementation) only when the class satisfies the following criteria:
1) "Is a special kind of," not "is a role played by a";
2) Never needs to transmute to be an object in some other class;
3) Extends rather than overrides or nullifies superclass;
4) Does not subclass what is merely a utility class (useful functionality you'd like to reuse); and
5) Within PD: expresses special kinds of roles, transactions, or things.
-- from Java Design: Building Better Apps and Applets (2nd Edition), by Peter Coad and Mark Mayfield

When to use inheritance and when not to?

I've just been trying find out when to use inheritance and when not to use inheritance? I know that inheritance gives advantages such as code reuse and maintainability. But when are their times not to use inheritance that may effect the design of a project?
Also when should one consider aggregation over inheritance(is-a relationship)?
thanks,
plandis

Hi
Answering this question usually requires a few books, so, I'm sorry, it's not really as simple as choosing between using a screwdriver vs. a hammer.
But, very short, inheritance should ideally only be used when there exist a strict 'is-a' relationship. However, sometimes it may be clever to inherit when you have a 'is-almost-a' relationship... And sometimes this is a stupid move. This depends on the context/circumstances.
Aggregation is normally considered a 'has-a' relationship, thereby differing clearly from inheritance. The old 'car' model says "a car is-a vehicle and has-some (at least) wheels."
The wheels are aggregated to the car class, that itself is inherited from vehicle.
However, this is just a good rule-of-thumb and there may be circumstantial reasons for not following these guidelines.

We have iPad2 and Macbook Pro. Both are registered to iTunes acct (same email address). We want to be able to use Facetime when she goes off to college. Any advise greatly appreciated!

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On your Mac, launch FaceTime and then go to the menubar for FaceTime->Preferences.
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Add another email address.
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Dear all
I need some advise on using DBMS_XA from PL/SQL with tightly coupled multiple branches under one global transaction. Basically, I've successfully written some PL/SQL code that in 3 different sessions attaches to 3 different branches of one global transaction and before ending each branch they can see each others uncommitted data. So far so good.
However, I'm not sure I completely understand how each branch must call xa_end, xa_prepare and xa_commit correctly using two phase commit and my calls result in errors like:
ORA-24767: transaction branch prepare returns read-only (XA error code 3 = Transaction was read-only and has been committed)
ORA-24756: transaction does not exist (XA error code -4 = XID is not valid)
ORA-02051: another session or branch in same transaction failed or finalized
This is the structure of my programs (3 SQL*Plus sessions):
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m1.xa_start tmnoflags
m2.DML
m3.Wait for thread A + B to manually be started and run xa_end
m4.xa_end tmsuccess
m5.xa_prepare
m6.xa_commit false
thread A: Uses xid 123|A (branch A of global transaction 123)
a1.xa_start tmnoflags
a2.DML -- thread A can see main and thread B's data
a3.xa_end tmsuccess
a4.xa_prepare -- required?
a5.Should we also call xa_commit false?
thread B: Uses xid 123|B (branch B of global transaction 123)
b1.xa_start tmnoflags
b2.DML -- thread B can see main and thread A's data
b3.xa_end tmsuccess
b4.xa_prepare -- required?
b5.Should we also call xa_commit false?
The failing steps are:
m5
m6
a4
a5
b4
b5
Before starting calling xa_end I see 3 rows in V$GLOBAL_TRANSACTION, eg (hex 7B = decimal 123):
FORMATID GLOBALID BRANCHID BRANCHES REFCOUNT PREPARECOUNT STATE FLAGS COUPLING
203348753 0000007B 00000000000000000000000000000000 3 3 0 ACTIVE 0 TIGHTLY COUPLED
203348753 0000007B 0000000000000000000000000000000A 3 3 0 ACTIVE 0 TIGHTLY COUPLED
203348753 0000007B 0000000000000000000000000000000B 3 3 0 ACTIVE 0 TIGHTLY COUPLED
Thanks a lot in advance.
Cheers
Finn

OK, I've figured it out. This is poorly documented as it's not well explained how to handle the various return codes. Turns out that all but the last xa_prepare calls return dbms_xa.xa_rdonly (tightly coupled branches are combined -- "read only" optimization), the last one returns dbms_xa.xa_ok and this is when you should call xa_commit.
Now my next problem is that DBMS_XA doesn't work from within jobs (DBMS_JOB and DBMS_SCHEDULER), which makes it very difficult to use DBMS_XA. My purpose of using DBMS_XA is to coordinate work across multiple sessions in one transaction but if I can't easily create the multiple sessions, I'm stuck.
When called from a job, xa_start throws:
ORA-24789: start not allowed in recursive call
on Oracle 11.2. In Oracle 11.1 it works, but xa_end fails with
ORA-25352: no current transaction
so I guess in fact the xa_start call didn't really work either, even though it returned tm_ok.
I'm now trying to find a workaround on how to use DBMS_XA from within jobs, please comment if you have any suggestions. Or if you have any suggestions on other means of establishing the concurrent sessions (I wouldn't like to resort to external programs that need username/password to connect as password management would be a security issue).
Thanks in advance.
Cheers
Finn

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Dear Chandramouli,
In the name you can use but in the no. not advisable I believe. When you are defining the no range, it is as following:
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We are working on a large pay/personnel management system and are
evaluating Forté Express and Sage Scaffolds. We need to answer some big
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out there with the answers.
1. How different can the database schema and the class model be, before
Express becomes a bad choice of framework? What solutions exist for cases
where Express is still a viable option?
2. Assuming that we can get around the problem in question 1, will the
Application Model features still work afterwards? (i.e. how sensitive are
the client-side services to changes in the database services?)
3. Express seems to use domain classes everywhere, whereas we are always
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this affect the performance of Express applications?
4. Has anybody out there used Sage Scaffolds on a large project recently?
How did it go? What problems should we watch out for? Doesn't its 'Chain
of Responsibility' pattern tend to produce a lot of unnecessary objects at
run-time?
5. Has anybody used the Born collection classes? How do they compare with
Brahma's Fortify?
Thanks to those who have already helped - all input gratefully received!
Tim Kimber
To unsubscribe, email '[email protected]' with
'unsubscribe forte-users' as the body of the message.
Searchable thread archive <URL:http://pinehurst.sageit.com/listarchive/>

I did all that before posting the orignial post..
declare
v_schema_exists varchar2(1) := 'N';
res             boolean;
schemaURL       varchar2(100) := 'T0090.xsd';
schemaPath      varchar2(100) := '/prmt/xsd/T0090.xsd'; --'/public/T0090.xsd';
xmlSchema xmlType := XMLTYPE(bfilename('DIR_PRMT_OUT_CVIEW','T0090.xsd'),NLS_CHARSET_ID('AL32UTF8'));
begin
begin
    select 'Y'
      into v_schema_exists
      from sys.all_xml_schemas -- changed from user_xml_schemas
     where schema_url = schemaURL;
    dbms_xmlSchema.deleteSchema(schemaURL,4);
    exception
      when NO_DATA_FOUND then
        null;
end;
if (dbms_xdb.existsResource(schemaPath)) then
    dbms_xdb.deleteResource(schemaPath);
end if;
res := dbms_xdb.createResource(schemaPath,xmlSchema);
dbms_xmlschema.registerSchema ( schemaURL, xdbURIType(schemaPath).getClob(), TRUE, TRUE, FALSE, TRUE );
end;
/ I guess my understanding was that I could grant another oracle user access to my registered schema just like I can grant a single user access to a table. Evidently I only have two options. Only the schema owner can use the schema or everyone can use the schema and I cannot grant access to a single user other than myself.
Edited by: Mark Reichman on Jul 2, 2010 9:08 AM
Edited by: Mark Reichman on Jul 2, 2010 9:09 AM

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http://www.actiontec.com/support/product_details.php?pid=41#q27
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Who uses inheritance?

I had a conversation with Tom Kyte on PL/SQL and OO (see thread http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:63942113457534#642059000346437745 ).
When I program in C#, I use a lot of inheritance and polymorphism, why not in PL/SQL?
Do you readers have good examples that show how you can use inheritance and polymorphism?
I hope that there will come support for encapsulation in Oracle Objects.

I like both, I like PL/SQL and I like C# (very OO).Like you, I like PL/SQL and I like OOPL's.
I don't know C# - I know C++, Java and Eiffel, but I'm not an expert.
In my opinion, Eiffel is the best OOPL (Eiffel was designed in 1985, commercialy released in 1986, ISO-standardized in 2006).
But mostly I like relational databases (relational DBMS's).
My motto is: “Thou shall not do in the Middle Tier, what thou could have done in the Data Tier”
(Toon Koppelaars in "A first JDeveloper project: Choices made, lessons learned", Oracle World 2002).
I think that the current object types in Oracle aren't practical for transient objects in PL/SQL,
first because a "true" OOPL must have references between transient objects (and then, perhaps, even a garbage collector).
Between the way, I sent my PL/SQL "wish list" to Steven Feuerstein’s site "21st Century PL/SQL"
(Add advanced O-O features like those found in Eiffel)
http://www.oracleplsqlprogramming.com/IC/ideas/data_structures_and_datatypes/object_types/index.php
Here are my attempts to use PL/SQL as OOPL ( PL/SQL++ :) :
Dynamic Method Dispatch and Method Overloading in a Subtype (May 2003)
http://www.quest-pipelines.com/newsletter-v4/0503_C.htm
Calling the Parent Object's Version of an Overridden Method
http://www.quest-pipelines.com/pipelines/plsql/tips03.htm#JUNE
(note: Oracle 11g has Generalized Invocation)
How to Get the Text Name of an Object's Type
http://www.quest-pipelines.com/pipelines/plsql/tips06.htm#JULY
The Template Design Pattern in PL/SQL
http://www.quest-pipelines.com/pipelines/plsql/tips06.htm#OCTOBER
Design by Contract (DBC) and PL/SQL
http://www.quest-pipelines.com/pipelines/plsql/tips.htm#JUNE
But, I think that Oracle object types are OK for persistent objects (for “column objects”, not for “row objects”).
C.J.Date in An introduction to Database Systems (2004, page 885) says:
"... object/relational systems ... are, or should be, basically just relational systems that support the relational domain concept (i.e., types) properly
- in other words, true relational systems, meaning in particular systems that allow users to define their own types".
Here is an attempt to use Oracle "object-relational" features "in the proper way" (in Date's sense) - to use object type as domain:
“OR(DBMS) or R(DBMS), That is the Question”
http://www.quest-pipelines.com/pipelines/plsql/tips.htm#OCTOBER
Regards,
Zlatko

Using Inheritance,dose child class have father 's inner class?

using Inheritance,dose child class have father 's inner class?

as near as I can tell, the conversation so far has been:
When I extend a class, does the subclass inherit the parent class's inner classes?
followed by
Never mind, i ran a test and found out the answer, sorry for my English.
hope that helped.
Lee

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Jay del Rosario wrote:
>
> How do I troubleshoot installation/distribution of a LabVIEW .exe
> which processes data using Matlab when it works on some computers but
> not others?
Poke around zone.ni.com and
http://digital.natinst.com/public.nsf/$$Search/ .
Good luck, Mark

Is it advisable to use inheritance when reusing dialogs/frames?

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