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Null, the Abyss @KeithYokoma - Drivemode, Inc. potatotips #17

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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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˒ˑˑˑˑ ˒ˑˑˑˑ ˒ˑˑˑˑ

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–Someone “A lot of sadness is coming from NullPointerException”

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Avoid NullPointerException • Null check for nullable value • Using support annotation • Using NullObject pattern • Returning null value • Null abyss in Android

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Null check statement public void method(Object arg) { if (arg == null) { throw new NullPointerException(); } // … }

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Null check statement public void method(Object arg) { if (arg == null) { throw new NullPointerException(); } // … }

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Null check statement ✓ Easy and basic way to avoid NPE ✗ Too many checks is bad for performance ✗ Need documentation for nullity ✗ Failure at runtime

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Support Annotations public void method(@Nullable Object arg) { if (arg == null) { Log.w(“Logger”, “Nothing I can do.”) return; } // … }

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Support Annotations public void method(@Nullable Object arg) { if (arg == null) { Log.w(“Logger”, “Nothing I can do.”) return; } // … }

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Support Annotations ✓ Gain Lint support for nullity ✓ Users can understand about nullity ✗ Still have possibility of null value ✗ Failure at runtime

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Using NullObject pattern ✓ No possibility of null value ✓ No change to get NullPointerException ✗ Need to learn architecture

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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; } }

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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; } }

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Returning null value Bad Practice public List get(int count) { if (something went wrong) { return null; } //… }

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Returning null value Good Practice public List get(int count) { if (something went wrong) { return new ArrayList<>(); } //… }

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Returning null value Other Good Practice public List get(int count) { if (something went wrong) { throw new SomeException(“Request failed for some reason.”); } //… }

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Returning null value • “null” means value is absent • Empty collection instead of null • Failure for throwing Exception

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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”

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For more details… • Effective Java

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Null, the Abyss @KeithYokoma - Drivemode, Inc. potatotips #17