Java 8 lamda expression : with return type with two arguments

interface Calculate{
public int add(int n1,int n2);
}
public class LambdaExpressionMultipleArg {
public static void main(String[] args) {
Calculate calc = (a,b) -> (a+b);
System.out.println(calc.add(10, 9));
}
}
output
19