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Null the abyss
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Keishin Yokomaku
May 13, 2015
Technology
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3k
Null the abyss
We need to look after 'null' value carefully.
Keishin Yokomaku
May 13, 2015
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Transcript
Null, the Abyss @KeithYokoma - Drivemode, Inc. potatotips #17
KeithYokoma Keishin Yokomaku Drivemode, Inc. Android Engineer GitHub: https://github.com/KeithYokoma Qiita:
http://qiita.com/KeithYokoma e-Book: http://amzn.to/1mZNydv
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–Someone “A lot of sadness is coming from NullPointerException”
Avoid NullPointerException • Null check for nullable value • Using
support annotation • Using NullObject pattern • Returning null value • Null abyss in Android
Null check statement public void method(Object arg) { if (arg
== null) { throw new NullPointerException(); } // … }
Null check statement public void method(Object arg) { if (arg
== null) { throw new NullPointerException(); } // … }
Null check statement ✓ Easy and basic way to avoid
NPE ✗ Too many checks is bad for performance ✗ Need documentation for nullity ✗ Failure at runtime
Support Annotations public void method(@Nullable Object arg) { if (arg
== null) { Log.w(“Logger”, “Nothing I can do.”) return; } // … }
Support Annotations public void method(@Nullable Object arg) { if (arg
== null) { Log.w(“Logger”, “Nothing I can do.”) return; } // … }
Support Annotations ✓ Gain Lint support for nullity ✓ Users
can understand about nullity ✗ Still have possibility of null value ✗ Failure at runtime
Using NullObject pattern ✓ No possibility of null value ✓
No change to get NullPointerException ✗ Need to learn architecture
Using NullObject pattern Bad Practice public enum NavMenu { HOME(R.id.home),
PROFILE(R.id.profile); public static NavMenu get(int id) { for (NavMenu menu : values()) { if (menu.id == id) return menu; } return null; } }
Using NullObject pattern Good Practice public enum NavMenu { HOME(R.id.home),
PROFILE(R.id.profile), NONE(-1); public static NavMenu get(int id) { for (NavMenu menu : values()) { if (menu.id == id) return menu; } return NONE; } }
Returning null value Bad Practice public List<Result> get(int count) {
if (something went wrong) { return null; } //… }
Returning null value Good Practice public List<Result> get(int count) {
if (something went wrong) { return new ArrayList<>(); } //… }
Returning null value Other Good Practice public List<Result> get(int count)
{ if (something went wrong) { throw new SomeException(“Request failed for some reason.”); } //… }
Returning null value • “null” means value is absent •
Empty collection instead of null • Failure for throwing Exception
Null abyss in Android • Some support API returns “null”
• e.g. MediaSessionCompat • You need to verify nullity for those APIs…
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–Someone “When you gaze into null, null gazes into you”
For more details… • Effective Java
Null, the Abyss @KeithYokoma - Drivemode, Inc. potatotips #17