Using Lambdas and Generics

Question

I am learning Java 8 and I am trying to use lambdas and generics together and I wrote this small example

import java.util.function.*;

public class LambdaTest<T> {

    public T calculate(T x, T y, BiFunction<T, T, T> func) {
        return func.apply(x, y);
    }

    public static void main(String args[]) {
        LambdaTest<Integer> l = new LambdaTest<Integer>();
        System.out.println("" + l.calculate(10, 10, (x, y) -> x + y));
        System.out.println("" + l.calculate(10, 10, (x, y) -> x * y));
        System.out.println("" + l.calculate(10, 10, (x, y) -> x / y));
        System.out.println("" + l.calculate(10, 10, (x, y) -> x - y));
        LambdaTest<Double> l2 = new LambdaTest<Double>();
        System.out.println("" + l2.calculate(10.0, 10.0, (x, y) -> x + y));
    }
}

Few questions I have are

1. My lambdas are being defined twice (x, y) -> x + y. is it possible to define these only once.

2. It seems that everytime this code is run, it will box 10 to Integer and then run the code. is it possible that I can define this for int rather than Integer. I tried doing new LambdaTest<int> but it did not work.

Answer 1

1. No. One is of type BiFunction<Integer, Integer, Integer>, whereas the other is of type BiFunction<Double, Double, Double>. They're thus not compatible with each other.
2. To avoid the unboxing and the boxing, you would have to use DoubleBinaryOperator and IntBinaryOperator, which use primitive types. But then you would need two different interfaces.