JDK11 - Local variables syntax for lambda parameters

21 Apr 2019 on Java

One of 90 features that have been introduced in JDK 11, is the support of the local variables as lambda parameters. This features was described in JEP-323: Local-Variables-Syntac for Lambda Parameters and can be considered as an extension of JEP-286: Local-Variable Type Inference. Now, the developes does not longer need to explicitly state the type of a local-variable but instead, use var as depicted in the code exceprt below, since it extends the use of this syntax to the parameters of Lambda expressions.

    List.of( "alfa", "bravo", "charlie", "delta", "echo", "foxtrot" ).stream()
            .filter( word -> ( word.length() & 1) == 1  )
            .map( (var word) -> word.toUpperCase() )
            .collect( toList() ).forEach( System.out::println );

This enhancement can be used when someone wants to add an annotation to the Lambda parameter. It was not possible to do this without a type being declared until the introduction of this JEP. To avoid having to use the explicit type we can use var to simplify things, as shown below:

List.of( "alfa", "bravo", "charlie", "delta", "echo", "foxtrot" )
    .stream()
    .filter( word -> ( word.length() & 1) == 1  )
    .map( ( @NotNull  var word ) -> word.toUpperCase() )
    .collect( toList() ).forEach( System.out::println );