Devoxx 2016 - day 2: notes (2016/11/08)

Array Linked to a List, the full story!

José Paumard

https://stuartmarks.wordpress.com/2015/12/18/some-java-list-benchmarks/
basic operations

• list.sort
• list.removeIf()
• forEach
• stream()
• ... random:
• arraylist
  • will never shrink
  • arraycopy operations
• http://www.hackersdelight.org/
• linkedlist:
  • som costly operations

benchmarks: JMH

• http://openjdk.java.net/projects/code-tools/jmh/
• annotation
• special maven rule create jar for benchmark
• @Param for measuring with different params
• @Benchmark

cpu architecture

• multicore cpu
• 3 levels of cache
• arraylist had contiguous zones
• linkedlist is penalized
  • pointer chasing
  • not cache-friendly
• other cache unfriendly examples:
  • SkipList
  • HashMap
• future:
  • http://mail.openjdk.java.net/mailman/listinfo/valhalla-spec-experts
  • Eclipse Collections
  • HPPC
  • Koloboke
  • Trove
  • http://java-performance.info/hashmap-overview-jdk-fastutil-goldman-sachs-hppc-koloboke-trove-january-2015/

Java 9

• List.of()
• Set.of()

demo

• removeIf() -- mark & sweep logic (BitSet)
• sort()
• Objects.requireNonNull() https://docs.oracle.com/javase/7/docs/api/java/util/Objects.html
• @FunctionalInterface https://docs.oracle.com/javase/8/docs/api/java/lang/FunctionalInterface.html
• Supplier interface https://docs.oracle.com/javase/8/docs/api/java/util/function/Supplier.html

---

Exploring Java 9

Venkat Subramaniam

Modularity

• big rt.jar split in modules ("jmods" subdir)
• java.base: default dependencies
• other code also in modules
• rule: no cycles (cyclic dependencies)

module

• collection of packages / data
• name
• "requires"
• "exports": only exported stuff can be used
• convention: put module in dedicated dir
• module-info.java in a top-level directory
  • module { export ; }
  • "requires java.base;" automatically added
• public is not "public" anymore -- module-bound
• examine dependencies
  • jdeps -s (exists since java 8)
  • -Xdiag:resolver
  • java -listmods -- JRE dependencies
• implied readability: support transitive dependencies
  • "requires public"
• transition to java 9:
  • jdeps -genmoduleinfo outputdir *.jar
  • put old jars in module path (-mp option)
  • "automatic modules"
  • uses name of jar instead of name of module"
  • classpath: "unnamed module" -- 'quarantined' module (exports all)
• versions: still ongoing

others

• jlink: create platformspecific binary executable -- "java"
• REPL "read evaluate print loop" -- jShell: snippets

---

The end of polling : why and how to transform a REST API into a Data Streaming API?

Audrey Neveu

"realtime user experience"

• no refresh buttons
• solutions
  • polling -- chatty protocol / inefficient
  • alternative
    • websockets RFC-6455
      • bidirectional
      • binary
      • reconfigure proxy
      • message layout not specified
      • new WebSocket(...)
      • connectionlost: not specified
    • server-sent events
      • text-only
      • data:
      • new EventSource(...)
      • callbacks: onopen/onMessage/onError
      • retry--config + recovery
      • use polyfills for IE
    • performance comparison: http://matthiasnehlsen.com/blog/2013/05/01/server-sent-events-vs-websockets/ 

demo with http://streamdata.io and a drone

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Open Sesame! Conversations With My Front Door

Maurice Naftalin

raspberry pi for controlling dooropener

• python
• asterisk: voip solution
  • complex setup / config
  • freepbx (commercial modules)
  • Asterisk-Java: support Fast AGI -- server on 45373
  • dialplay: voice recognition -- IBM Watson speech recognition service for converting the codes
  • DTMF is more reliable for entering a code future:
  • Natural Language Processing

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Notes on Type Theory for absolute beginners

Hanneli Tavante

intro to Type theory
steps:

• collect all keywords / analyse gramar
• replace with mathemetics
• remove duplicates
• symbolic logic
• environment (set of classes / variables)
• predicate logic to analyse your system
• lambda calculus
• ...