|NO.Z.00016|——————————|BigDataEnd|——|Hadoop&Scala.V03|——|Scala.v03|Scala函数|where表达式|

一、while 表达式

### --- while表达式

~~~     Scala提供了与 Java 类似的while和do...while循环。
~~~     while语句的本身没有任何返回值类型，即while语句的返回结果是Unit类型的 () 。
~~~     Scala内置控制结构特地去掉了 break 和 continue。

### --- 特殊情况下如果需要终止循环，可以有以下三种方式：

~~~     使用Boolean类型的控制变量
~~~     使用return关键字
~~~     使用breakable和break，需要导入scala.util.control.Breaks包

### --- where编程示例

~~~     # while循环
var flag = true
var result = 0
var n = 0
while (flag) {
    result += n
    n += 1
    println("res = " + result)
    println("n = " + n)
    if (n == 10) {
        flag = false
    }
}

// for循环
var flag = true
var res = 0
for (i <- 0 until 10 if flag) {
    res += i
    println("res = " + res )
    if (i == 5) flag = false
}

/**
* 1 + 2 + 3 + 4
*
* @return
*/

def addInner() {
    for (i <- 0 until 10) {
        if (i == 5) {
            return
        }
        res += i
        println("res = " + res)
    }
}
def main(args: Array[String]): Unit = {
    addInner()
}
def main(args: Array[String]): Unit = {
    
// 需要导包
    import scala.util.control.Breaks._
    var res = 0
    breakable {
    for (i <- 0 until 10) {
        if (i == 5) {
            break
        }
        res += i
    }
}
println("res = " + res)
}

### --- 编程代码

package yanqi.cn.part02

object WhileDemo {
  def main(args: Array[String]): Unit = {
    var num = 1
    //    while (num < 10) {
    //      println(s"num = $num")
    //      num += 1
    //    }
    //    do {
    //      println(s"num = $num")
    //      num += 1
    //    } while (num < 10)

    //使用Boolean类型的控制变量，终止循环
    //    var flag = true
    //    while (flag) {
    //      println(s"num = $num")
    //      num += 1
    //      if(num==5) flag=false
    //    }

    //使用return关键字终止循环
    //    for (i <- 1 to 10) {
    //      if (i == 5) return
    //      println(s"i=$i")
    //    }

    //使用breakable和break终止循环，需要导入scala.util.control.Breaks包
    import scala.util.control.Breaks._
    var res = 0
    breakable {
      for (i <- 1 until (10)) {
        if (i == 5) break()
        res += i
      }
    }
    println(res)
  }
}

### --- 编译打印

D:\JAVA\jdk1.8.0_231\bin\java.exe "-javaagent:D:\IntelliJIDEA\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=52870:D:\IntelliJIDEA\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath D:\JAVA\jdk1.8.0_231\jre\lib\charsets.jar;D:\JAVA\jdk1.8.0_231\jre\lib\deploy.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\access-bridge-64.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\cldrdata.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\dnsns.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\jaccess.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\jfxrt.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\localedata.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\nashorn.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunec.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunjce_provider.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunmscapi.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\sunpkcs11.jar;D:\JAVA\jdk1.8.0_231\jre\lib\ext\zipfs.jar;D:\JAVA\jdk1.8.0_231\jre\lib\javaws.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jce.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jfr.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jfxswt.jar;D:\JAVA\jdk1.8.0_231\jre\lib\jsse.jar;D:\JAVA\jdk1.8.0_231\jre\lib\management-agent.jar;D:\JAVA\jdk1.8.0_231\jre\lib\plugin.jar;D:\JAVA\jdk1.8.0_231\jre\lib\resources.jar;D:\JAVA\jdk1.8.0_231\jre\lib\rt.jar;E:\NO.Z.10000——javaproject\NO.Z.00002.Hadoop\ScalaPro\out\production\ScalaPro;D:\JAVA\scala-2.12.2\lib\scala-library.jar;D:\JAVA\scala-2.12.2\lib\scala-reflect.jar yanqi.cn.part02.WhileDemo
10

Process finished with exit code 0

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Walter Savage Landor:strove with none,for none was worth my strife.Nature I loved and, next to Nature, Art:I warm'd both hands before the fire of life.It sinks, and I am ready to depart

                                                                                                                                                   ——W.S.Landor

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