主要方法在Scala [英] main method in Scala

问题描述

我写了一个scala类并定义了main（）方法。它编译，但是当我运行它，我得到NoSuchMethodError：main。在所有的scala示例中，我已经看到，主要方法是在一个对象中定义的。在Java中，我们在类中定义main方法。是否可以在scala类中定义main（），或者我们总是需要一个对象？

I wrote a scala class and defined the main() method in it. It compiled, but when I ran it, I got NoSuchMethodError:main. In all the scala examples, I have seen, the main method is defined in an object. In Java we define the main method in a class. Is it possible to define main() in a scala class or do we always need an object for this?

感谢

推荐答案

正如尤金在评论中说，在Scala中没有静态方法。但请注意：

As Eugene said in a comment, there are no static methods in Scala. But watch this:

$ cat Echo.scala
object Echo {
  def main( args:Array[String] ):Unit = args foreach println
}

$ scalac Echo.scala

$ javap Echo\$.class
Compiled from "Echo.scala"
public final class Echo$ {
  public static final Echo$ MODULE$;
  public static {};
  public void main(java.lang.String[]);
}

$ javap Echo.class
Compiled from "Echo.scala"
public final class Echo {
  public static void main(java.lang.String[]);
}

请注意，Echo类的classfile（不是Echo $，确实有一个public static void main方法。 Scala为在对象中定义的方法生成与Java兼容的静态方法。

Note that the classfile for the Echo class (not Echo$, the object) does indeed have a public static void main method. Scala generates static methods for methods defined in objects for compatibility with Java.

但是，我认为在Scala程序中创建一个主要的方法。使用应用程序特征;它更干净：

However, I consider creating a main method in a Scala program an anachronism. Use the App trait instead; it's cleaner:

object Echo extends App {
  args foreach println
}

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