scala(五)Learn CH7 Programming in Scala from others

scala(5)Learn CH7 Programming in Scala from others
scala(5)Learn CH7 Programming in Scala from others
CH7 Build-in control structure
If statement
package com.sillycat.easyscala.lesson5

object TestIf {

  def main(args: Array[String]): Unit = {
        var filename = "default.txt"
        println(args.isEmpty)
        if (!args.isEmpty){
            filename = args(0)
        }
        println("filename: " + filename)

        //if statement will return the last sentence
        val filename2 =
            if (args.isEmpty) "default.txt" else args(0)
        println ("filename2: " + filename2)
    }
}

If statement has a return value.

For Statement
package com.sillycat.easyscala.lesson5

object TestFor {

  def main(args: Array[String]): Unit = {
    val files = (new java.io.File(".")).listFiles()
    println("==========file names1 :")
    for (file <- files) {
      print(file + " ")
    }
    println();
    println("==================================");

    println("==========file names2 :")
    for (f <- files) print(f + " ")
    println();
    println("====================================");
   
    // 1 to 5 will return Range(1, 6)
    // 1, 2, 3, 4, 5
    println("==========numbers 1 :")
    for (i <- 1 to 5) print(i + " ")
    println();
    println("=======================================");
   
    // 0 until 5 will return Range(0, 5)
    // 0, 1, 2, 3, 4
    println("===========numbers 2: ");
    for (i <- 0 until 5) print(i + " ")
    println();
    println("============================");

    // multiple checkpoint
    for (
      file <- files if (file.getName.endsWith("bin"))
    ) println(file)

    // for
    for (
      file <- files
      if (file.isFile)
      if (file.getName.endsWith("gitignore"))
    ) println(file)

    //put all the matched files in array
    val sfiles = for (
      file <- files if (file.isFile)
    ) yield file

    // files in array
    for (i <- 0 to sfiles.length - 1){
      print(sfiles(i))
    }

  }

}

Try Catch System almost the same to Java
package com.sillycat.easyscala.lesson5
import java.io.FileReader

object TestTry {

  def main(args: Array[String]): Unit = {
    var f = new FileReader("test.txt")
    try {
      // use the file
    } catch {
      case ex: java.io.FileNotFoundException =>
        println(ex)
      case ex: java.io.IOException =>
        println(ex)
    } finally {
      f.close()
    }
  }

}

Match is much better than switch, not matter int, even string is working.
package com.sillycat.easyscala.lesson5

object TestMatch {

  def main(args: Array[String]): Unit = {
    val firstArg = if (!args.isEmpty) args(0) else ""
    var n = 10000
    var friend = "adsfadfasf"
    firstArg match {
      case "salt" =>
        friend = "pepper"
         n = 100
      case "chips" =>
        friend = "salsa"
        n = 10
      case "eggs" =>
        friend = "bacon"
        n = 1
      //this is the default value
      case _ =>
        friend = "huh?"
        n = 0
    }
    println(friend + n.toString());
  }

}





references:
http://sillycat.iteye.com/blog/1536392

http://snowriver.org/blog/tag/scala/
http://snowriver.org/blog/2011/03/20/programming-in-scala-%E5%AD%A6%E4%B9%A0%E7%AC%94%E8%AE%B0ch7-built-in-control-structure/