Scala in Impatient 习题解答9 文件和正则表达式A1

本章又发现原版正确而中文版翻出来的错误

val tokens = source.mkString.split("\\S+")
                                      ^ 应为小写

1. import scala.io.Source
   import java.io.PrintWriter
   
   object Run extends App { 
       val fileName = args(0)
       val sources = Source.fromFile(fileName)
       val out = new PrintWriter(fileName + ".reverse")
       sources.getLines.toArray.reverse.foreach(l => out.println(l))
       out.close
   }
   

2. import scala.io.Source
   import java.io.PrintWriter
   
   object Run extends App { 
       val fileName = args(0)
       val sources = Source.fromFile(fileName)
       var str = ""
       for (chr <- sources) {
           if (chr == '\t') str += "  "
           else str += chr
       }
       sources.close
   
       val out = new PrintWriter(fileName)
       out.print(str)
       out.close
   }
   

3. 用一行完成有奖励

    io.Source.fromFile("filename").mkString.split("\\s+").foreach(s => if (s.length > 12) println(s))
   

4. 从只包含浮点数的文本文件中读取数字。

    val floats = io.Source.fromFile("floats.txt").mkString.split("\\s+").map(_.toFloat)
   
    println(floats.sum)
    println(floats.sum / floats.size)
    println(floats.max)
    println(floats.min)
   

5. 答案稍微有点不完美， 第一行应该都是1， 目前不知道除了判断1之外，还有什么优雅的方式 翻了一下别人的解答， BigDecimal(2).pow(n)可以解决这个问题

    import java.io.PrintWriter
   
    object Run extends App { 
        val fileName = args(0)
        val out = new PrintWriter(fileName)
        for (n <- 0 to 20) out.println(makeStr(n))
        out.close
   
        def makeStr(n: Int) = {
            val t = math.pow(2, n)
            " " * 10 + math.pow(2, n).toInt + " " * (11-t.toString.size) + 
            math.pow(2,-n) 
        }
    }
   

6. 仔细对照了英文版，发现or的字体是一起的。所以认为是搜索整串。

    import scala.io.Source
    import java.io.PrintWriter
   
    object Run extends App { 
        val fileName = args(0)
        val sources = Source.fromFile(fileName)
        val pat = """"like this, maybe with \" or \\"""".r
   
        for (line <- sources.getLines) {
            for (mth <- pat.findAllIn(line)) println(mth)
        }
   
        sources.close
    }
   

7. 正则写了好久- -!! 重点在于匹配所有不是浮点数的token。类似20这样的在这里我认 为是整数，不是浮点数。

    import scala.io.Source
   
    object Run extends App { 
        val fileName = args(0)
        val sources = Source.fromFile(fileName)
        val pat = """^((?!^[-]?\d*\.\d+$).)+$""".r
   
        for (token <- sources.mkString.split("""\s+""")) {
            for (mth <- pat.findAllIn(token)) println(mth)
        }
   
        sources.close
    }
   

测试用文件abc.txt的内容

    $ cat abc.txt
    sd2.1fsd 843 48,34.locs njv lbxc.74.32 q50ijnls
    n 3.493 , 3490-.a 21 .3 -2.5 988.0 a! (b&^bb) 2..10

执行结果

    $ scala Run abc.txt
    sd2.1fsd
    843
    48,34.locs
    njv
    lbxc.74.32
    q50ijnls
    n
    ,
    3490-.a
    21
    a!
    (b&^bb)
    2..10

1. val pat = """<img.*?src=["'](.+?)["'].*?>""".r
   for (pat(src) <-
     pat.findAllIn(io.Source.fromURL("http://www.baidu.com").mkString)) {
     println(src)
   }
   

执行结果 $ scala run.scala http://www.baidu.com/img/bdlogo.gif http://www.baidu.com/cache/global/img/gs.gif

1. 编译后调用scala Run /home .class

    import java.io._
   
    object Run extends App {
      val file = new File(args(0))
      val ext = if (args.size > 1) args(1) else ""
   
      val allDirs = if (file.isDirectory) Iterator[File](file) ++ subdirs(file, ext)
      else subdirs(file, ext)
   
      allDirs.foreach(dir => for (f <- dir.listFiles(new FileFilter() {
          override def accept(file: File):Boolean = {
            if(ext != null) file.getName.endsWith(ext) else true
          }
        })) println(f))
   
      def subdirs(dir: File, ext: String): Iterator[File] = {
        val child = dir.listFiles.filter(_.isDirectory)
        child.toIterator ++ child.toIterator.flatMap(subdirs(_, ext))
      }
    }
   

2. 这个直接抄书了

   import java.io._
   
   class Person(val name: String) extends Serializable{
     private var friend: String = ""
   
     def makeFriend(p: Person){
       friend = p.name
     }
     def currentFriend = friend
   }
   object Run extends App {
     val p1 = new Person("jintao")
     val p2 = new Person("jinping")
     val jmu = new Person("jmu")
   
     jmu.makeFriend(p2)
     p2.makeFriend(p1)
   
     val persons = Array[Person](p1, p2, jmu)
     val out = new ObjectOutputStream(new FileOutputStream("/tmp/peoples"))
     out.writeObject(persons)
     out.close
   
     val in = new ObjectInputStream(new FileInputStream("/tmp/peoples"))
     val savedPersons = in.readObject.asInstanceOf[Array[Person]]
   
     println(savedPersons(2).name)
     println(savedPersons(2).currentFriend)
   }