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 program −
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);
}
}
Limitations
There are certain limitations on using var in lambda expressions.
1. var parameters cannot be mixed with other typed parameters. Following will throw compilation error.
(var a, String b) -> a.toLowerCase() + b.toLowerCase();
Error:
'var' cannot be mixed with non-var parameters
2. var parameters cannot be mixed with other parameters. Following will throw compilation error.
(var a, b) -> a.toLowerCase() + b.toLowerCase();
Error:
Syntax error on token "var", ( expected after this token
Syntax error on token "->", invalid AssignmentOperator
Syntax error, insert ")" to complete Expression
3. var parameters can only be used with parenthesis. Following will throw compilation error.
var a -> a.toLowerCase();
Error:
Syntax error, insert ":: IdentifierOrNew" to complete ReferenceExpression
Syntax error, insert ";" to complete LocalVariableDeclarationStatement
Syntax error, insert "AssignmentOperator Expression" to complete Expression
