Stream.reduce(Float,BinaryOperator) BinaryOperator 指的是哪个功能接口方法？

Question

例如，

List<Product> productsList = new ArrayList<Product>();  
productsList.add(new Product(1,"HP Laptop",25000f));  
productsList.add(new Product(2,"Dell Laptop",30000f));  
productsList.add(new Product(3,"Lenevo Laptop",28000f));  
productsList.add(new Product(4,"Sony Laptop",28000f));  
productsList.add(new Product(5,"Apple Laptop",90000f));  

Float totalPrice = productsList.stream()  
                               .map(product->product.price)  
                               .reduce(0.0f,(sum, price)->sum+price);   
System.out.println(totalPrice); 

这里(sum, price)->sum+price指的是哪个功能接口？

Answer 1

查看 Stream Javadoc：

T reduce(T identity, BinaryOperator<T> accumulator)

(sum, price)->sum+price 在您的示例中实现了 BinaryOperator<Float>。

这个功能接口有一个方法接受两个相同类型的参数（Float 在你的例子中）和 returns 一个相同类型的结果。

Answer 2

因为你提到了 "functional interface method": reduce is actually calling apply of BiFunction (from which BinaryOperator extends).