Scala 不能乘以 Java Doubles? [英] Scala can't multiply java Doubles?

问题描述

在 Scala 中使用 Java 类时，我注意到 Scala 不能乘以 Java Doubles.举个例子:

While working with a Java class in Scala, I noticed that Scala can't multiply Java Doubles. Here's an example:

scala> val x:java.lang.Double = new java.lang.Double(34.0)
x: java.lang.Double = 34.0

scala> val y:java.lang.Double = new java.lang.Double(2.1) 
y: java.lang.Double = 2.1

scala> x*y
<console>:7: error: value * is not a member of java.lang.Double
       x*y
        ^

哇！我猜这是因为 Scala 运算符只是方法，所以它试图调用 Java Double 类的乘法方法(即34.0.*(2.1)").哎呀.有没有一种简单的方法来执行此互操作?

Whoa! I guess it's because Scala operators are just methods, so it's trying to call the multiply method of the Java Double class (ie, "34.0.*(2.1)"). Oops. Is there an easy way to do this interop?

推荐答案

我会定义一个到 Scala 的隐式转换 Double

I would define an implicit conversion to a Scala Double

implicit def javaToScalaDouble(d: java.lang.Double) = d.doubleValue

现在您的代码可以运行了！类似的表达式如 1.2 + x 也可以使用.并且由于自动装箱代码，如下所示确实不需要隐式转换即可编译.

Now your code works! And similarly expressions like 1.2 + x work as well. And due to auto-boxing code like the following does compile without requiring implicit conversions.

def foo(d: java.lang.Double) = println(d)
val z: scala.Double = 1.2
foo(z)

--弗拉维乌·西皮根

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