[英]Why no promotion when adding ints to List<Double>
in Java I created an ArrayList of Double and I invoked the method list.add(1), however, I get an error. 在Java中,我创建了一个Double的ArrayList,并调用了方法list.add(1),但是,出现错误。 If I can assign an int to a double variable like this: double num = 1;
如果我可以将int分配给double变量,例如:double num = 1; due to automatic promotion, then why can't I add a 1 to ArrayList of Double via automatic promotion?
由于自动升级,为什么我不能通过自动升级为Double的ArrayList添加1?
You're not trying to convert int
to double
; 您不是要将
int
转换为double
; you're trying to convert int
to Double
, which is a combination of boxing and the implicit conversion from int
to double
. 您正在尝试将
int
转换为Double
,这是装箱和从int
到double
的隐式转换的组合。 That doesn't work, even in a simple assignment: 即使在简单的任务中,这也不起作用:
// Error: incompatible types: int cannot be converted to Double
Double num = 1;
It doesn't even work for Long
- you need to specify a long
literal: 甚至对于
Long
也不起作用-您需要指定一个long
文字:
Long num1 = 1; // Invalid
Long num2 = 1L; // Valid
In your case, you just need to use a double
literal, eg 在您的情况下,您只需要使用
double
精度字面量,例如
list.add(1.0);
list.add(1D);
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