代码之家 › 专栏 › 技术社区 › Srinivas

scala中伴随对象的问题

scala

1

Srinivas · 技术社区 · 8 年前

下面的代码编译得很好(这是一个简单的伴生对象教程)

scala> :paste
// Entering paste mode (ctrl-D to finish)

trait Colours { def printColour: Unit }
object Colours {
private class Red extends Colours { override def printColour = { println ("colour is Red")} }
def apply : Colours = new Red
}

// Exiting paste mode, now interpreting.

defined trait Colours
defined object Colours

当我尝试时

val r = Colours

r.printColour

我出错了

<console>:17: error: value printColour is not a member of object Colours
   r.printColour

2 回复 | 直到 8 年前

1

2

prayagupa soxunyi 8 年前

val r = Colours ,这不是你的电话 apply 因为apply方法没有参数,所以它不接受params ()

参见示例,

class MyClass {
  def doSomething : String= "vnjdfkghk"
}

object MyClass {
  def apply: MyClass = new MyClass()
}

MyClass.apply.doSomething shouldBe "vnjdfkghk" //explicit apply call

val r = Colours.apply

( 空paren ),这样你就不需要打电话了 .apply 明确地

如。

class MyClass {
  def doSomething : String= "vnjdfkghk"
}

object MyClass {
  def apply(): MyClass = new MyClass()
}

MyClass().doSomething shouldBe "vnjdfkghk"

非常有用的资源

Difference between function with parentheses and without [duplicate]

Why does Scala need parameterless in addition to zero-parameter methods?

Why to use empty parentheses in Scala if we can just use no parentheses to define a function which does not need any arguments?

2

1

jwvh 8 年前

将括号添加到 apply

def apply(): ...

…和 Colours 对象调用。

val r = Colours()

然后它将按需要工作。

r.printColour  // "colour is Red"