Local Variable Type Infrerence: Friend or Foe.

on YouTube ↗46m

" summary

Local variable type inference (var) in Java SE 10 infers concrete types from initializers but has concrete gotchas: must initialize var and null and array initializers rejected (e.g. new int[] works but {1,2,3} doesn't), numeric literals infer int (breaking byte/short/long-sized protocols), lambdas and polyexpressions need explicit target types, and combining diamond + var can infer Object for generics (PriorityQueue<Integer> becomes PriorityQueue<Object>). JDK11 adds var lambda params for annotations; use var where the RHS clearly shows the type and avoid it when inference changes semantics (overloads, masking, serialization).

AI-written summary · about

" chapters (18)

1. 0:00Introduction
2. 2:20Java Variables
3. 4:00Local Variable Type Infrerence
4. 6:07Simple Uses
5. 12:29Final NonFinal
6. 14:31Action of the Distance
7. 17:09Edge Cases
8. 20:00Null
9. 25:49Beware of multiple type inference
10. 28:13Polymorphism
11. 30:36Lambda Expression
12. 32:39Type Infrerence
13. 33:47Generics
14. 37:17Inner Classes
15. 38:36Reserved Types
16. 40:19var
17. 42:50var vs int
18. 44:52Summary

" related talks

• 57mLocal variable type inference: Friend or foe?Simon Ritter · JPoint 2019
• 55mLocal Variable Type Inference: Friend or Foe?Simon Ritter · Developer Summit 2020
• 46mType Inference: Friend or FoeVenkat Subramaniam · Oracle Code One 2018
• 39mVar with Style: Local Variable Type Inference in JavaStuart Marks · Oracle Code One 2018
• 53mFun with var in Java 11Nicolai Parlog · J-Fall 2018
• 01h 00mJava Language Futures - All Aboard Project AmberBrian Goetz · Devoxx Belgium 2017
• 36mWhat’s New in the Java Platform Language and Tooling AreaMichel Trudeau · Oracle Code One 2018
• 16mThe past, present and future of the Java type systemAlasdair Collinson · Devoxx Belgium 2019