PROPOSAL: 'final' without explicit type

[Gabriel Belingueres]

VariableInitializer type is neither primitive nor Object. Why?

Also, there are times when it might be OK to assign null to a variable
as long as the compile time type can be uniquely identified:

final a = (booleanCondition) ? null : new SomeClass();

In this case the you can assume that the type of variable a will be SomeClass.

What about autoboxing?

final a = (booleanCondition) ? 1 : new Integer(2);

it is int or Integer? (currently the ? operand resolve it to an int)

Also see my notes on the interaction between final variables and overloading:
http://mail.openjdk.java.net/pipermail/coin-dev/2009-March/000859.html

IMO, when using the ? operator it should not try to find an
intersection type for the compile time type of the final variable, but
it should be the exact type on both the 2nd and 3rd operand, otherwise
it should raise a compiler error. If you want another type for the
variable, then specify it as usual.

2009/3/26 Marek Kozieł <develop4lasu at gmail.com>:
> AUTOHOR: Laau aka Marek Kozieł
>
> FEATURE SUMMARY:
>
> MAJOR ADVANTAGE:
> It allows people to concentrate on logic during operating on heavy
> generics and to use values which are more intuitive for them than
> variables.
>
> MAJOR BENEFIT(s):
> It allows to avoid duplicating unnecessarily types of declaration.
> It increasea concentration on 'what I've got' than on 'what type is
> that' (we decrease size by one to obtain last element index, not
> because we can do this = it's int), while for variables we still keep
> concentrate on: 'what type is that' / 'what I can put there'.
> Editing existing code to get some value is easier.
> That method can be itself multi-thread with this, but it's a far future.
> Using of Generics is easier.
>
>
> MAJOR DISADVANTAGE:
> Certainly, some people will overuse this solution.
> It might be a problem if a person does not know how to give proper
> names for values.
>
> ALTERNATIVES:
> Normal variables.
>
>
> EXAMPLES
>
> SIMPLE / ADVANCED EXAMPLE:
>  public Map<String,ArrayList<String>> readMaping(){
>    final map = new HashMap<String,ArrayList<String>>();
>    for( final row : readLine() ){
>       String key = row.get(0);
>       row.remove(0);
>       map.put(key, row);
>    }
>    return map;
>  }
>
>  public Map<String,ArrayList<String>> readMaping(){
>    final map; //compile time error
>    map= new HashMap<String,ArrayList<String>>();
>    for( final row : readLine() ){
>       String key = row.get(0);
>       row.remove(0);
>       map.put(key, row);
>    }
>    return map;
>  }
>
> public class Final {
>  static final maping = new HashMap<String, ArrayList<String>>();
> }
>
> public class Final {
>  static final maping = (Map<String,ArrayList<String>>)loadMap();
> }
>
> DETAILS
>
> SPECIFICATION: FieldDeclaration
>  FieldDeclaration would be extended to allow omitting Type
> declaration if field is final and it's directly followed by assignment
> of new class instance creation(created object type would be used), or
> of CastExpression (JLS 15.16) (ReferenceType would be used).
>
> SPECIFICATION: LocalVariableDeclarationStatement
>  (JLS 14.4) Local Variable Declaration Statements would be extended
> to allow omitting Type declaration if field is final and listed rules
> taking place:
> - VariableInitializer appears.
> - Variable is not initialized directly with null.
> - VariableInitializer type is neither primitive nor Object.
> - If VariableInitializer -Expression type is intersection type (we
> always ommit Object type in intersection), then:
>  --> If intersected types have common ancestor then this ancestor is
> used as type.
>  --> If effect of intersected types is one Interface, then this
> interface is used as type.
>  --> In other way, an error occurs.
>
>
> COMPILATION:
>  Just as today, value type only need to be determined.
>  For first implementation this solution can omit supporting intersections.
>
> TESTING:
> The same as final-s variables.
>
> LIBRARY SUPPORT:
> No.
>
> REFLECTIVE APIS:
> No.
>
> OTHER CHANGES:
> No.
>
> MIGRATION:
> None.
>
> COMPATIBILITY
> Only code is no forward compatible.
>
> REFERENCES
>
> http://bugs.sun.com/view_bug.do?bug_id=4459053
>
> http://bugs.sun.com/view_bug.do?bug_id=4983159
>
> http://lasu2string.blogspot.com/2009/03/final-without-explicit-type-proposal.html
>
>
>
> PS. Personally I think that consider operator is better, but I'll take
> time to improve this proposal while it's more Java-like.
>
> --
> Pozdrowionka. / Regards.
> Lasu aka Marek Kozieł
>
> http://lasu2string.blogspot.com/
>
>