[英]Custom Collector Implementation for summing float java 8
I am trying to create a custom float addition similar to Collectors.summingDouble()
.我正在尝试创建一个类似于
Collectors.summingDouble()
的自定义浮动添加。
But I am facing 2 issues and I am not sure about how to fix it.但我面临两个问题,我不确定如何解决它。
BiConsumer
- Line #27 - void methods cannot return a value BiConsumer
- 第 27 行 - void 方法不能返回值Collectors.of
- Line#32 - The method of(Supplier, BiConsumer<R,T>
, BinaryOperator<R>
, Collector.Characteristics...) in the type Collector is not applicable for the arguments ( Supplier<Float[]>
, BiConsumer<Float,Employee>
, BinaryOperator<Float>
) What needs to be done here for fixing the issue? Collectors.of
- 第 32 行 - Collector 类型中的 (Supplier, BiConsumer<R,T>
, BinaryOperator<R>
, Collector.Characteristics...) 方法不适用于 arguments ( Supplier<Float[]>
, BiConsumer<Float,Employee>
, BinaryOperator<Float>
) 这里需要做什么来解决这个问题?public class CustomCollector {
public static void main(String[] args) {
Employee e1=new Employee(1,"Tom",10.2f);
Employee e2=new Employee(1,"Jack",10.4f);
Employee e3=new Employee(1,"Harry",10.4f);
ArrayList<Employee> lstEmployee=new ArrayList<Employee>();
lstEmployee.add(e1);lstEmployee.add(e2);lstEmployee.add(e3);
/* Implementation 1
* double totalSal=lstEmployee.stream().collect(Collectors.summingDouble(e->e.getSal()));
System.out.println(totalSal);
*/
//Implementation 2
Function<Employee,Float> fun=(e)->e.getSal();
BiConsumer<Float,Employee> consumer=(val,e)->val+e.getSal();
BinaryOperator<Float> operator=(val1,val2)->val1+val2;
Supplier<Float[]> supplier=() -> new Float[2];
float FtotalSal=lstEmployee.stream().collect(
Collector.of(supplier,consumer,operator));
System.out.println(FtotalSal);
}
}
class Employee {
int id;
String name;
float sal;
// getters, setter, constructror
}
It seems, you are confusing Reduction with Mutable Reduction .看来,您将Reduction与Mutable Reduction混淆了。
Your functions, (val, e) -> val + e.getSal()
and (val1, val2) -> val1 + val2)
, are suitable for a Reduction operation, but not for collect
.您的函数
(val, e) -> val + e.getSal()
和(val1, val2) -> val1 + val2)
适用于归约操作,但不适用于collect
。 The supplier, producing a Float[]
array of length two, doesn't fit to it at all.供应商生产一个长度为 2 的
Float[]
数组,根本不适合它。
Eg, you can perform your operation using例如,您可以使用
float f = lstEmployee.stream().reduce(
0F,
(val, e) -> val + e.getSal(),
(val1, val2) -> val1 + val2);
This bears some boxing overhead, as all intermediate sums are represented as Float
objects.这会带来一些装箱开销,因为所有中间和都表示为
Float
对象。
You can avoid this using Mutable Reduction , when you create a mutable container which is capable of holding a float
value without boxing, ie new float[1]
.您可以使用Mutable Reduction来避免这种情况,当您创建一个能够在不装箱的情况下保存
float
值的可变容器时,即new float[1]
。 Then, you have to supply functions accepting an array argument and changing the contained value.然后,您必须提供接受数组参数并更改包含值的函数。 Since your intended result is a
float
, rather than an array, you further need a finisher to produce the final result.由于您的预期结果是
float
,而不是数组,因此您还需要一个整理器来产生最终结果。
float f = lstEmployee.stream().collect(
Collector.of(
() -> new float[1], // a container capable of holding one float
(floatArray,e) -> floatArray[0] += e.getSal(), // add one element to the array
(a1, a2) -> { a1[0] += a2[0]; return a1; }, // merge two arrays
array -> array[0]) // extracting the final result value
);
Of course, this is only for exercising, as you have already shown to know a simpler solution using builtin features.当然,这仅用于锻炼,因为您已经展示了使用内置功能了解更简单的解决方案。
If getting the sum is the focus.如果得到总和是重点。 You could try something like below.
你可以试试下面的东西。
float FtotalSal = (float) lstEmployee.stream().mapToDouble(e -> e.getSal()).sum();
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