[英]How to call scala's Option constructors from Java
I am working on a mixed java/scala project, and I am trying to call a scala object's method from Java. 我正在研究一个混合的java / scala项目,我试图从Java调用scala对象的方法。 This method takes an Option[Double]
as a parameter. 此方法将Option[Double]
作为参数。 I thought this would work: 我认为这会奏效:
Double doubleValue = new Double(1.0);
scalaObj.scalaMethod(new Some(doubleValue));
But Eclipse tells me "The constructor Some(Double) is undefined". 但Eclipse告诉我“构造函数Some(Double)未定义”。
Should I be calling the constructor for scala.Some
differently? 我应该调用scala.Some
的构造函数。 scala.Some
不同?
In Scala you normally lift to Option as follows: 在Scala中,您通常会按如下方式升级到Option:
scala> val doubleValue = Option(1.0)
doubleValue: Option[Double] = Some(1.0)
()
is a syntactic sugar for apply[A](A obj)
method of Option
's companion object. ()
是Option
的伴随对象的apply[A](A obj)
方法的语法糖。 Therefore, it can be directly called in Java: 因此,它可以直接在Java中调用:
Option<Double> doubleValue = Option.apply(1.0);
You can construct a Some instance that way, this compiles for me, 你可以用这种方式构造一个实例,这为我编译,
Some<Double> d = new Some<Double>(Double.valueOf(1));
The problem may be the missing generics, try doing, 问题可能是缺少的泛型,尝试做,
scalaObj.scalaMethod(new Some<Double>(doubleValue));
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