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OLIVIER TABONE Co-fondateur / Directeur
[email protected] 06 83 01 05 76
A few words about
JAVA’S FINAL KEYWORD
RMS TechTalk #2 - 19.10.2016
TechTalk #2 - 19.10.2016
OLIVIER TABONE Co-fondateur / Directeur
A FEW WORDS ABOUT
Java’s Final Keyword
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THE FINAL KEYWORD
TechTalk #2 - 19.10.2016
Provide a form of immutability to the Java language. So what ? OLIVIER TABONE Co-fondateur / Directeur
Enforce immutability at compile time So what ? Programming errors are prevented by the compiler
A FEW WORDS ABOUT
Java’s Final Keyword
So what ? Less crash in the application So I write better code if I use the final keyword ? Yes! 7
TechTalk #2 - 19.10.2016
THE FINAL KEYWORD (The bad)
OLIVIER TABONE Co-fondateur / Directeur
Applies to class, members, variables and methods Semantics varies !
A FEW WORDS ABOUT
Java’s Final Keyword
Benefits varies ! Performance varies !
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TechTalk #2 - 19.10.2016
FINAL VARIABLES use when required
The variable must be assigned once and only once. OLIVIER TABONE Co-fondateur / Directeur
A FEW WORDS ABOUT
Java’s Final Keyword
Immutable value semantics for raw types (long, int, …) As java has no immutability for reference types, this is kind of useless. No performance benefits (on Dalvik + ART/AOT + ART/JIT) ‣ Use when required = Anonymous inner class definition ‣ Use when variable’s scope is large and you want to prevent a reassignment by mistake 9
TechTalk #2 - 19.10.2016
FINAL MEMBERS private final static
OLIVIER TABONE Co-fondateur / Directeur
Use to define constants. Constants are immutable, right ?
A FEW WORDS ABOUT
Java’s Final Keyword
10
TechTalk #2 - 19.10.2016
FINAL MEMBERS private final
OLIVIER TABONE Co-fondateur / Directeur
Provide atomicity for object creation. Object is wether fully created or not.
A FEW WORDS ABOUT
Java’s Final Keyword
a class with only final immutable members is immutable ! 11
TechTalk #2 - 19.10.2016
OLIVIER TABONE Co-fondateur / Directeur
FINAL MEMBERS
Use as much as possible *, immutability is good design. * can’t be used in Activity and Fragment subclasses :-(
A FEW WORDS ABOUT
Java’s Final Keyword
no performance benefits
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TechTalk #2 - 19.10.2016
FINAL CLASS
Designed for inheritance or not OLIVIER TABONE Co-fondateur / Directeur
A FEW WORDS ABOUT
Java’s Final Keyword
Classes are designed to be inherited or not to be inherited. If you don’t know, your class is not designed to be inherited. using the “final class” modifier indicates your class is not designed to be inherited. final class should be the default 13
TechTalk #2 - 19.10.2016
FINAL CLASS
Do not design for inheritance OLIVIER TABONE Co-fondateur / Directeur
A FEW WORDS ABOUT
Java’s Final Keyword
Inheritance is hard Inheritance is fragile Inheritance takes time Inheritance will make you sad Design for Inheritance is the exception. final class is the norm.
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TechTalk #2 - 19.10.2016
FINAL CLASS
Provide some performance gains OLIVIER TABONE Co-fondateur / Directeur
A FEW WORDS ABOUT
Java’s Final Keyword
Performance benefits with ART/AOT (Android 6) No performance benefits for other virtual machines : Dalvik (Android < 6) Hotspot (Desktop) ART/JIT (Android 7)
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TechTalk #2 - 19.10.2016
TAKE AWAYS DO use final keyword…
OLIVIER TABONE Co-fondateur / Directeur
…for classes to restrict inheritance …for members so that objects are fully initialized …for static member so that constants are immutable
A FEW WORDS ABOUT
Java’s Final Keyword
DONT use final keyword… …for variable (unless required) …invoking a performance gain 16
Merci de votre participation !
OLIVIER TABONE Co-fondateur / Directeur
[email protected] 06 83 01 05 76
Créateur d’applications mobiles
