jdt embraces lambda expressions - eclipsecon north america 2014

EclipseCon NA 2014 | JDT Embraces Lambda Expressions

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Srikanth SankaranIBM India

Stephan HerrmannGK 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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http://download.eclipse.org/eclipse/downloads/

http://download.eclipse.org/eclipse/updates/4.3-P-builds/






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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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jdt embraces lambda expressions - eclipsecon north america 2014

Technology

eclipsecon na

readonly string o

parse tree

nonnull string

o changes

o abstractions

list compile

world view