The document presents an overview of Java 8 features related to lambda expressions, method references, and type annotations as discussed in a session at EclipseCon NA 2014. It outlines advancements in the Java Development Tools (JDT) as they adapt to these new language features and emphasizes various potential issues during type inference and software package assimilation. The presentation includes technical details and examples related to the implementation of these Java features.

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Srikanth Sankaran
IBM India
Stephan Herrmann
GK Software
Noopur Gupta
IBM India

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Java 8 features:
JSR335 - Project Lambda
 Lambda Expressions & Method References
 Extensions to
Overload resolution & Type inference
 Support for “code carrying” interface methods.
JSR308 - Type Annotations
JEP120 - Repeating Annotations
JEP118 - Method Parameter Reflection
JSR269 - Pluggable Annotation Processor API &
javax.lang.model API enhancements for Java 8

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LambdaExpression ::= LambdaParameters '->' LambdaBody
LambdaParameters -> BeginLambda LambdaParameterList
LambdaParameterList -> '(' FormalParameterListopt ')„
LambdaBody -> Expression
LambdaBody -> Block
I i = BeginLambda (x) -> { };

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Scanning + Parsing => Parse tree
+ Resolution => Resolved parse tree
+ Data/control flow analysis => Flow analyzed parse tree
+ Code generation => Class files.
() -> { throw new Exception(); } is void and value compatible.

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o Changes the very notion of a type.
o Some subsystems should view @NonNull String != @ReadOnly String
o while others should view them as being the same.
o Abstractions need to support either world view efficiently.
String is a String is a String

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Collectors.<Person,String,Integer>toMap(..)
Collectors.toMap(..)
Collector<String,Integer> coll = new MyCollector<>();

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 Recipe for disaster:
● implement java.util.List → compile against JRE 7 → OK
● upgrade to JRE 8 but compile as 1.7
 Undefined compiler behavior
● 1.7 compiler cannot handle default methods (from .class)
● exact answer depends on compiler implementation details
● there is no specification
● ecj and javac differ
● assimilation is difficult

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Enter
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Lambda Expression:
Method Reference:

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Demo
Examples:

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Far too risky to
cram late into 8
(Nov 2013)

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List <: List<String> ?
Raw types

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“Problem detected during type inference: ...”

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Dramatis personæ - The usual suspects
Jay Arthanareeswaran
Deepak Azad
Shankha Banerjee
Anirban Chakarborty
Vikas Chandra
Noopur Gupta
Ayushman Jain
Manju Mathew
Manoj Palat
Srikanth Sankaran
Sarika Sinha
Jesper S. Møller
Stephan Herrmann
Markus Keller
Dani Megert
Andy Clement
Steve Francisco
Michael Rennie
Olivier Thomann
Curtis Windatt
Walter Harley
David Williams

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