Devoxx 2009: Project Coin

18/11/2009, Joe D. Darcy, Sun

slides: http://blogs.sun.com/darcy/entry/project_coin_devoxx_2009

Project Coin

• small language changes in JDK7
• keep broad consideration of java landscape → remain consistent with the Java Language
• bigger language changes, not in scope of Project Coin
  • JSR308: annotations to improve static checkers (e.g. @NotNull)
  • JSR294: modularity

principles of Project Coin:

• reading more important than writing
  • 'beautiful' code
  • don't hide what's happening
• simplicity matters
• no slash-and-burn: remember broad user-base
• balance stability versus progress
• prefer library / IDE changes over language changes (String.join)
• no new keywords
• no type system changes
• small in specification, implementation and testing

methodology:

• open: blog entries / white board on Devoxx2008
• call for proposals
• prototypes recommended
  • lot of work
  • very beneficial → learn / find issues
• existing requests for enhancement: 120 changes → too much

final list of Project Coin enhancements

• numbers:
  • binary notation: 0b00100100001
  • group numbers with '_': long big = 1_123_456_789;
• switch on a String – really cool!
  • specification: only one word added
  • proposal contains a suggested implementation:
    • uses String.hashCode() for an initial switch
  • big patch in javac
  • lots of tests to validate change
    • reject pre -source 7 classes
    • null behavior
    • hash collisions
    • fall-throughs
    • → comparable to enum switch control flow
• diamond <> operator : type interference → e.g. Map <String,String> map = new HashMap<>();
  • a lot of prototyping work
  • quantitative analysis
  • some concerns on language evolution were considered
• JSR292: invokedynamic for dynamic languages
• auto-close of Closable types within a special try block (ARM)
  • try(File f = new File) {} → f is automatically closed when leaving the block
• simplified varargs method invocation, working along with generics
• language support for Lists and Maps:
  • List<String> list = [“1”, “2”];
  • list[0]
  • map{“hello”}

not retained in Project coin:

• Elvis operator:
  • use ?: as a shorthand for testing on null
  • conclusion from building a prototype→ doesn't fit well in java
• multiple exception handling
  • disjunctive means of | operator
• properties:
  • changes the type system
  • a lot of work (e.g. reflection api, corner cases …) – the 'enum' specification is demonstrated as a comparable change that involved a lot of rework
  • pseudo-properties workaround: via annotation-processing → Project Lombok
• reified generics
  • source language compatibility issues – java generic erasure was chosen for backward compatibility
  • C# created a separate generic library
  • difficult for other languages to target the a platform with reified generics
• extensible enums
  • most enums are constant
  • low utility