Better Java with “less” noise

Neeraj Bhusare@NeerajBhusareZafin Labs

Agenda

1. Xtend introduction2. Active Annotations3. Extension methods 4. With operator, Lambda expressions5. Switch expressions

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.

Xtend ?

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

Active AnnotationsLightweight code generation

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.

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.

Observable

Observable (Lightweight)

SWTBot

SWTBot (Lightweight)

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.

Extension methodsAdding methods to existing types

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

SWT

SWT (using Extension methods)

Runtime library of extension methods

● org.eclipse.xtext.xbase.lib.ObjectExtensions● IterableExtensions● MapExtensions ● ListExtensions ● CollectionExtensions ● BooleanExtensions ● IntegerExtensions ● FunctionExtensions.

With operatorBinding objects to lambda expressions

with operator (=>/double-arrow operator)

● Allows you to bind objects to the scope of lambda expression so that you can perform some operations on itnew 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.

SWT

SWT (using with operator)

Implicit ‘it’ param and syntactic sugar

Lambda expressionsLess verbose lambdas

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 ( ) braces3. 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

( ) braces3. Lambda is a block expressions. No

semicolons4. Parameter name is optional. Implicit

variable “it” is used.

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)

Switch expressionUber switch

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)

Switch expressionsType Guard

Fall Through

References

Documentationhttps://eclipse.org/xtend/documentation/Presentation’shttp://goo.gl/AlWDkBBlog’shttps://oehme.github.io/http://blog.efftinge.de/2012/12/java-8-vs-xtend.htmlSource codehttps://github.com/oehme/xtend-contribhttps://github.com/joergreichert/ActiveAnnotationsExamples

Questions ?