Black monkey house: Scala for expression patterns

We traverse Map collection when, in fact, had already learned a

println("for表达式中的模式")
//for中匹配会自动忽略失败的匹配
println("scala.collection.JavaConverters._-------------------")
// Java 转 Scala
import scala.collection.JavaConverters._
for((k,v) <- System.getProperties.asScala){
  println(k + " -> " + v)
}

println("scala.collection.JavaConversions._----------------------")
import scala.collection.JavaConversions._
for((k,v) <- System.getProperties){
  println(k + " -> " + v)
}

println("k------通过匹配模式取value为空的key----------------")
for((k,"") <- System.getProperties.asScala){
  println(k)
}

println("v==''--------通过守护模式取value为空的key-----------")
for ((k,v) <- System.getProperties.asScala if v == ""){
  println(k,v)
}

尖叫提示：for中匹配会自动忽略失败的匹配，如果匹配失败，会continue，但是match匹配，如果失败，就报异常了

Reproduced in: https: //www.jianshu.com/p/73856bce81c2