Talk on the Xtend project at Eclipse Day India 2016

1. Better Java with “less” noise
Neeraj Bhusare
@NeerajBhusare
Zafin Labs

2. Agenda
1. Xtend introduction
2. Active Annotations
3. Extension methods
4. With operator, Lambda expressions
5. Switch expressions

3. Xtend ?
● Xtend is a statically typed programming language
● It is an “extension” to Java and NOT a replacement
● It fully supports all the Java idioms
● It allows usage of existing Java API in much nicer way without any
interoperability issues
● Provides additional features like - Type Inference, Extension methods,
Lambda expressions, Active annotations...
● Latest release - Xtend 2.9.0.

4. Xtend ?
● It is implemented in Xtext and is a proof of concept of how involved a
language implemented in Xtext can be.

5. Active Annotations
Lightweight code generation

6. Active Annotations
● Code written using Xtend gets translated to Java
● The translation process can be “altered” using Active annotations
● Mainly used to generate boilerplate Java code; that otherwise is coded
manually.

7. Active annotation (Syntax)
● Annotation which is itself annotated with Active
@Active(SWTBotProcessor)
annotation SWTBot { }
● @Active takes a Annotation Processor as the parameter
● It can either be declared in Java or Xtend.

8. Observable

9. Observable (Lightweight)

10. SWTBot

11. SWTBot (Lightweight)

12. Existing Active annotation
● org.eclipse.xtend.lib.annotations
○ @Accessor - Adds getter and or setter methods for your fields
○ @Data - Turns an annotated class into Value object class. Generates - final fields, getter
methods, constructor with parameters, equals, hashCode and toString methods
○ @FinalFieldsConstructor - Creates a constructor that takes a parameter for each final
field of a class.
○ @EqualsHashCode - Creates default implementation for equals and hashCode.

13. Extension methods
Adding methods to existing types

14. Extension methods
● Allows you to add additional methods to an existing type without modification
"hello".toFirstUpper() // calls
StringExtensions.toFirstUpper("hello")
● Based on a simple syntactic trick: The method is called with the first
argument as its receiver
entity.save(comment) // persistenceManager.save(entity,
comment);
● Resulting code is much more readable

15. SWT

16. SWT (using Extension methods)

17. Runtime library of extension methods
● org.eclipse.xtext.xbase.lib.ObjectExtensions
● IterableExtensions
● MapExtensions
● ListExtensions
● CollectionExtensions
● BooleanExtensions
● IntegerExtensions
● FunctionExtensions.

18. With operator
Binding objects to lambda expressions

19. with operator (=>/double-arrow operator)
● Allows you to bind objects to the scope of lambda expression so that you can
perform some operations on it
new Button(parent, style) =>
[text = “Hello World” enabled = false]
● The operator => passes the left expression as a parameter to the lambda on
the right. The result of this operation is the object itself.

20. SWT

21. SWT (using with operator)

22. Implicit ‘it’ param and syntactic sugar

23. Lambda expressions
Less verbose lambdas

24. Java 8 vs. Xtend (subtle differences)
shapes.forEach(
s -> { s.setColor(RED);}
);
1. Represented using arrow ->
2. The ( ) braces are mandatory. Lambda
needs to be passed inside ( ) braces
3. The body of the lambda needs to be inside
curly braces { } and semicolons are
mandatory
4. Parameter names (s) is mandatory.
shapes.forEach[color = RED]
1. Represented using square brackets [ ]
2. Not mandatory. However, you can use the
( ) braces
3. Lambda is a block expressions. No
semicolons
4. Parameter name is optional. Implicit
variable “it” is used.

25. Java 8 vs. Xtend (type inference, less verbose)
Java :
List<Album> sortedFavs = albums.stream()
.filter(a -> a.tracks.anyMatch(t -> (t.rating >= 4)))
.sorted(comparing(a -> a.name))
.into(new ArrayList<>());
Xtend :
val sortedFavs = albums.stream
.filter[tracks.anyMatch[rating >= 4]]
.sorted(comparing[name])
.into(newArrayList)

26. Switch expression
Uber switch

27. Switch expressions
● Not limited to certain values. It can be used for any object reference
● For case expression of type boolean, the case matches if the expression
evaluates to true, for other types main expression is compared using
Object.equals (Object)

28. Switch expressions
Type Guard
Fall Through

29. References
Documentation
https://eclipse.org/xtend/documentation/
Presentation’s
http://goo.gl/AlWDkB
Blog’s
https://oehme.github.io/
http://blog.efftinge.de/2012/12/java-8-vs-xtend.html
Source code
https://github.com/oehme/xtend-contrib
https://github.com/joergreichert/ActiveAnnotationsExamples

30. Questions ?