Doubts on casting concepts in TAW12 part 1

Can someone help me clarify a little confusion on Casting in materials provided by SAP Education on TAW12 part 1.
I attended ILT and my instructor emphasized that: "wherever in this material we read 'Up-cast' or 'Down-cast', we should consider this as an error because what they meant to say is exactly the opposite".
This has now left me confused especially after revising.
Can someone please share some light on these terminologies and concept? especially in relation to materials provided on TAW12 ABAP Workbench Concept Part 1 (2013 SAP AG. All rights reserved)
I have not been able to find much materials online for this section of the book and for many others.
Any help would be greatly appreciated.
Vince

Hi Vince,
               First thing, STOP worrying about the SAP material whether the contain is right/wrong.
              Now, what I understand is that the instructor tried to explain the concepts in a easy way to remember but has that seems to have messed up your basics on up-cast & down-cast.
I have looked in my sap material ( but its 2005 SAP AG reserved ). The definition are fine.
Anyways I'll try to explain in my style:
Narrow casting( up-casting ):- Assigning of a subclass instance to a reference variable of type " reference to super class ". Here we navigate from a more detailed view to one with less details.
Widening Cast( down-cast ):- Assigning a super class to a sub class. From a less detailed view to more detailed view.
                         SUPER CLASS( vehicle ) less details
                                   |
                                   |
                                   |
                            SUB CLASS ( car, truck, bus, bike ) more details
PS:- Try to understand the meaning from the example and then go back to the definition in the material.

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Although this step is optional, Oracle recommends that an online redo log be created when a standby database is created. By following this best practice, a standby database will be ready to quickly transition to the primary database role.
...

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2 IS
3
4     PROCEDURE sp_mem(mCursor sys_refcursor,MemberId INTEGER);
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6
7 END;
8 /
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tylerd@DEV2>
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2 IS
3
4     PROCEDURE sp_mem(mCursor sys_refcursor,MemberId INTEGER)
5     IS
6
7     BEGIN
8
9             NULL;
10
11     END;
12
13     PROCEDURE sp_mem(mCursor sys_refcursor, mEmailId INTEGER)
14     IS
15
16     BEGIN
17
18             NULL;
19
20     END;
21
22 END;
23 /
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ORA-06550: line 1, column 7:
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HTH
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Message was edited by:
David Tyler
Oops, copied the wrong bit of the output! :-)

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1>
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I read one of the SCJP 6 exam book, when talking about Set, it gives one definition:
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Edited by: roamer on 2009?10?23? ??10:29

jverd wrote:
endasil wrote:
When using HashSet or LinkedHashSet, the objects you add to them must override hashCode(). If they don't override hashCode(), the default Object. hashCode() method will allow multiple objects that you might consider "meaningfully equal" to be added to your "no duplicates allowed" set.This really is completely wrong. Duplicates being added to your set has nothing to do with not overriding hashCode, and everything to do with not overriding equals. No, if you override equals but not hashCode, you can get dupes. That is, two items that your equals method says are equal can make it into the Set.Sorry, to clarify, what I meant by that was that to avoid duplicates of meaningfully equal objects, you must override equals, and overriding hashCode is just a consequent of overriding equals (to maintain the equal objects have equal hashcodes invariant). Overriding hashCode alone will not, and cannot, prevent meaningfully equal duplicates if you don't first define meaningfully equal by overriding equals.
In summary, it's wrong because
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2) If you have any other definition of meaningfully equal that you want enforced in a Set, you must override equals to correspond to that definition.
3) If you override equals, you must override hashCode by the contract of hashCode and equals.
That's why I was saying that the statement was completely wrong. It's taking a backwards approach.
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Edited by: endasil on 26-Oct-2009 1:11 PM

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I am using NW 7.1 trial version. when I try to do a simple ALV prog in WebDyn .
DATA: lr_column_settings TYPE REF TO if_salv_wd_column_settings,
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its working in ECC6.0
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Hi,
You should ask your question in the right forum which should be *Web Dynpro Abap".
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we have another class called Dog which has a method callled bark().
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kirn291 wrote:
Dog d=new Animal();
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I understood the widening cast concept. i want to know in what scenarios, the usage of widening cast makes sense. does the widening improve performance of the program? is there any scenario where we MUST use the widening cast in the logic? i want to understand how do we justify the usage of widening cast.
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thanks

As for the thread's question: you use it when you have a subclass instance being pointed at by a superclass reference, and you need to access subclass specific components.
Adding about widening / down cast:
I repeat: you don't have choice.
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* Using downcasting
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DATA lo_structdescr TYPE REF TO cl_abap_structdescr.
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ENDTRY.
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* Alternative way using dynamic calling
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CATCH cx_sy_dyn_call_error.
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Edited by: Alejandro Bindi on Mar 31, 2010 5:47 PM
As you can see I got confused by the narrowing / widening terms as well. I also found out the terms upcast / downcast to be much easier to understand.

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Hi Experts,
I've got few doubts understanding the concepts of Locking.
I'm referring this article - http://docs.oracle.com/cd/E14072_01/server.112/e10592/ap_locks001.htm
1]
>
When a transaction obtains a row lock for a row, the transaction also acquires a table lock for the table in which the row resides.
The table lock prevents conflicting DDL operations that would override data changes in a current transaction.
>
What is the significance of the 2 ^nd^ line? Does that mean, at that time we can't DROP or ALTER the table structure ??
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2]
>
A row share lock (RS), also called a subshare table lock (SS), indicates that the transaction holding the lock on the table has locked some rows in the table and intends to update them, as is the case in a SELECT ... FOR UPDATE statement. An SS lock is the least restrictive mode of table lock, offering the highest degree of concurrency for a table.
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>
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3]
>
A share table lock (S) held by one transaction allows other transactions to query the table but allows updates only if a share table lock is held by only a single transaction. Multiple transactions may hold a share table lock concurrently, so holding this lock is not sufficient to ensure that a transaction can modify the table.
A share row exclusive table lock (SRX), also called a share-subexclusive table lock (SSX), is more restrictive than a share table lock. Only one transaction at a time can acquire an SSX lock on a given table. An SSX lock held by a transaction allows other transactions to query or lock specific rows using SELECT ... FOR UPDATE, but not to update the table.
An exclusive table lock (X) is the most restrictive mode of table lock, allowing the transaction that holds the lock exclusive write access to the table. Only one transaction can obtain an X lock for a table.
>
I'm also little confused with these locking types and not able to understand the difference practically. I know these are very important concepts and should not be neglected.
Can any one please help me understand these concepts?
Thanks In Advance,
Ranit B.
Edited by: ranit B on Nov 28, 2012 6:47 PM
-- added [3]

padders wrote:
Does that mean, at that time we can't DROP or ALTER the table structure Yes, that's pretty much what it means.
What is the need of an SX lock when it allows other transactions to manipulate data?As the text says - the lock allows concurrent update of other rows - i.e. you lock some row(s) but other rows can still be updated.Thanks Padders.
But then, what is the difference between SS and SX? Both allow other rows to be updated.
Please rectify me if I'm wrong.
I got some idea. It would be really helpful if you could please give me some pointers on the other doubts also?

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hi,
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Doubts on casting concepts in TAW12 part 1

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