[Java lista] final formalis parameter

[Zoltan Mozes]

szia!

Egyrészt optimálisabb lesz (C esetén ilyenkor ha tudja, akkor proci-regiszterbe teszi ehlyből, nem stack/heap whatever , hogy java-nál hogy van azzal kapcsolatban majd tapasztaltabban kisegítenek minket :))

Thinking in Java idevonatkozó része: (jó, static-ról beszél, na) :L)
"static final variables can be optimized by the JVM to improve program speed. Program constants should thus be declared as static and final. "

Sokkal fontosabb hogy ha nem fog változni a metóduson belül akkor azért (si) érdemes finalt-t elétenni (és itt jön be a Thinking in Java és főle persze MÁS könyvek is), mert ez közelebb viszi a kódodat a DBC szemléletű fejlesztéshez.

DBC == Design By Contract, aminek egyik eleme az amiről msot beszélünk:

"Invariants" = a metódustörzsben jelen esetben. (assert ill/és/vagy final)

(de a kék+zöld könyv is jó, csak abból ilyeneket nem fogsz kiolvasni...)
Persze mindig az a kérdés hogy mi a cél.


szóval az idevonatkozó rész:
" Design by Contract (DBC) is a concept developed by Bertrand Meyer, creator of the Eiffel programming language, to help in the creation of robust programs by guaranteeing that objects follow certain rules that cannot be verified by compile-time type checking.[93] These rules are determined by the nature of the problem that is being solved, which is outside the scope of what the compiler can know about and test."

(...)itt ugrunk pár bekezdést(...)
 
"
Invariants
An invariant gives guarantees about the state of the object that will be maintained between method calls. However, it doesn't restrain a method from temporarily diverging from those guarantees during the execution of the method. It just says that the state information of the object will always obey these rules: Feedback


Upon entry to the method. 
Before leaving the method.
In addition, the invariant is a guarantee about the state of the object after construction. Feedback


According to the this description, an effective invariant would be defined as a method, probably named invariant( ), which would be invoked after construction, and at the beginning and end of each method. The method could be invoked as:


assert invariant();


This way, if you chose to disable assertions for performance reasons, there would be no overhead at all. Feedback

"

Best Regards,
Zoltán Mózes


EPAM Systems
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-----Original Message-----
From: javalist-bounces at javagrund.hu [mailto:javalist-bounces at javagrund.hu] On Behalf Of Jabba Laci
Sent: Thursday, December 14, 2006 9:52 PM
To: java
Subject: [Java lista] final formalis parameter

Sziasztok!

Ha a formalis parameterben final-t hasznalunk, akkor az optimalisabb
(gyorsabb) kodot fog eredmenyezni? Szamos esetben biztosan tudom, hogy
a formalis parameter erteke fix, nem valtozik a fuggvenyben. Ilyenkor
erdemes eletenni a "final"-t?

Egy eroltetett pelda:

public int mult(int x) {
   return 2 * x;
}

vagy:

public int mult(final int x) {
   return 2 * x;
}

Azon tul, hogy a 2. esetben x erteket nem lehet megvaltoztatni, mi még
a kulonbseg?

      Koszonettel:

                Lac
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