Scala example source code file (App.scala)

This example Scala source code file (App.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

app, array, array, delayedinit, delayedinit, listbuffer, listbuffer, long, unit, unit

The Scala App.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2002-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */
package scala

import scala.compat.Platform.currentTime
import scala.collection.mutable.ListBuffer

/** The `App` trait can be used to quickly turn objects
 *  into executable programs. Here is an example:
 *  {{{
 *    object Main extends App {
 *      Console.println("Hello World: " + (arguments mkString ", "))
 *    }
 *  }}}
 *  Here, object `Main` inherits the `main` method of `App`.
 *
 *  `args` returns the current command line arguments as an array.
 *    
 *  @author  Martin Odersky
 *  @version 2.1, 15/02/2011
 */
trait App extends DelayedInit {

  /** The time when the execution of this program started, in milliseconds since 1
    * January 1970 UTC. */
  val executionStart: Long = currentTime

  /** The command line arguments passed to the application's `main` method.
   */
  protected def args: Array[String] = _args

  private var _args: Array[String] = _

  private val initCode = new ListBuffer[() => Unit]

  /** The init hook. This saves all initialization code for execution within `main`.
   *  This method is normally never called directly from user code.
   *  Instead it is called as compiler-generated code for those classes and objects
   *  (but not traits) that inherit from the `DelayedInit` trait and that do not themselves define
   *  a `delayedInit` method.
   *  @param body the initialization code to be stored for later execution
   */
  override def delayedInit(body: => Unit) {
    initCode += (() => body)
  }

  /** The main method.
   *  This stores all argument so that they can be retrieved with `args`
   *  and the executes all initialization code segments in the order they were
   *  passed to `delayedInit`
   *  @param args the arguments passed to the main method
   */
  def main(args: Array[String]) = {
    this._args = args
    for (proc <- initCode) proc()
    if (util.Properties.propIsSet("scala.time")) {
      val total = currentTime - executionStart
      Console.println("[total " + total + "ms]")
    }
  }
}