减少 int[] 数组时出现“错误：找不到合适的减少方法”

Question

鉴于这种实现总和的尝试：

int[] nums = { 1,3,4,5,7};
var sum = Arrays.asList(nums).stream().reduce(0,(a,b)->a+b);          

以下问题通常是由于提供给编译器的类型信息不足以进行类型推断。但是这里我们有一个明确的 int[] 数组作为源。为什么会出现这个错误？

Line 3: error: no suitable method found for reduce(int,(a,b)->a + b)
        var sum = Arrays.asList(nums).stream().reduce(0,(a,b)->a+b);
                                              ^
    method Stream.reduce(int[],BinaryOperator<int[]>) is not applicable
      (argument mismatch; int cannot be converted to int[])
    method Stream.<U>reduce(U,BiFunction<U,? super int[],U>,BinaryOperator<U>) is not applicable
      (cannot infer type-variable(s) U
        (actual and formal argument lists differ in length))
  where U,T are type-variables:
    U extends Object declared in method <U>reduce(U,BiFunction<U,? super T,U>,BinaryOperator<U>)
    T extends Object declared in interface Stream

Answer 1

var sum = Arrays.asList(nums) 返回一个 List，因此 reduce 方法将 int[] 添加到 int[]，这是不允许的，会导致编译错误。

这是一个可能的解决方案：

    int[] nums = { 1,3,4,5,7};
    var sum= Arrays.stream(nums).reduce(0,(a,b)->a + b);

或

var result = Arrays.stream(nums).sum();