Java 11 - Use of Var in Lambda Expressions

Java 11 allows to use var in a lambda expression and it can be used to apply modifiers to local variables.

 (@NonNull var value1, @Nullable var value2) -> value1 + value2 

Consider the following example −

ApiTester.java

 import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; @interface NonNull {} public class APITester { public static void main(String[] args) { List<String> tutorialsList = Arrays.asList("Java", "HTML"); String tutorials = tutorialsList.stream() .map((@NonNull var tutorial) -> tutorial.toUpperCase()) .collect(Collectors.joining(", ")); System.out.println(tutorials); } } 

Output

 Java HTML 

Limitations

There are certain limitations on using var in lambda expressions.

• var parameters cannot be mixed with other parameters. Following will throw compilation error.

 (var v1, v2) -> v1 + v2 

• var parameters cannot be mixed with other typed parameters. Following will throw compilation error.

 (var v1, String v2) -> v1 + v2 

• var parameters can only be used with parenthesis. Following will throw compilation error.

 var v1 -> v1.toLowerCase()