How to multiply key * value in Map in Java?

I have this class:

class Product {
    public double price;

    public Product(double price) {
        this.price = price;
    }
}

And a Map:

Map<Product, Integer> products = new HashMap<>();

That contains several products added like so:

products.put(new Product(2.99), 2);
products.put(new Product(1.99), 4);

And I want to calculate the sum of all products multiple the values using streams? I tried:

double total = products.entrySet().stream().mapToDouble((k, v) -> k.getKey().price * v.getValue()).sum();

But doesn’t work. Thanks

I expect:

(2.99 * 2) + (1.99 * 4) = 5.98 + 7.96 = 13.94

>Solution :

The stream of entries needs single parameter lambda for each entry, not (k,v):

double total = products.entrySet().stream().mapToDouble(e -> e.getKey().price * e.getValue()).sum();