为什么 Scala 在类名的末尾放置一个美元符号? [英] Why does Scala place a dollar sign at the end of class names?

问题描述

在 Scala 中，当您查询对象的类或类名时，您将在打印输出的末尾得到一个恶意美元符号 ("$"):

In Scala when you query an object for either its class or its class name, you'll get a rogue dollar sign ("$") at the tail end of the printout:

object DollarExample {
  def main(args : Array[String]) : Unit = {
    printClass()
  }

  def printClass() {
    println(s"The class is ${getClass}")
    println(s"The class name is ${getClass.getName}")
  }
}

结果为:

The class is class com.me.myorg.example.DollarExample$
The class name is com.me.myorg.example.DollarExample$

当然，手动删除末尾的$"很简单，但我想知道:

Sure, it's simple enough to manually remove the "$" at the end, but I'm wondering:

• 为什么会在那里?;和
• 无论如何要配置 Scala"以省略它?

• Why is it there?; and
• Is there anyway to "configure Scala" to omit it?

推荐答案

您在这里看到的原因是 scalac 将每个 object 编译为两个 JVM 类.末尾带有 $ 的那个实际上是实现实际逻辑的真正的单例类，可能是从其他类和/或特征继承的.没有 $ 的是一个包含 static 转发器方法的类.我认为这主要是为了 Java 互操作.也因为你实际上需要一种在 Scala 中创建静态方法的方法，因为如果你想在 JVM 上运行一个程序，你需要一个 public static void main(String[] args) 方法作为入口点.

What you are seeing here is caused by the fact that scalac compiles every object to two JVM classes. The one with the $ at the end is actually the real singleton class implementing the actual logic, possibly inheriting from other classes and/or traits. The one without the $ is a class containing static forwarder methods. That's mosty for Java interop's sake I assume. And also because you actually need a way to create static methods in scala, because if you want to run a program on the JVM, you need a public static void main(String[] args) method as an entry point.

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

object Main { def main(args: Array[String]): Unit = ??? }

// Exiting paste mode, now interpreting.


scala> :javap -p -filter Main
Compiled from "<pastie>"
public final class Main {
  public static void main(java.lang.String[]);
}

scala> :javap -p -filter Main$
Compiled from "<pastie>"
public final class Main$ {
  public static Main$ MODULE$;
  public static {};
  public void main(java.lang.String[]);
  private Main$();
}

我认为您对此无能为力.

I don't think there's anything you can do about this.

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