【Scala十一】Scala核心五：case模式匹配
编程技术 / houtizong 发布于 3年前 56
package spark.examples.scala.grammars.caseclassesobject CaseClass_Test00 { def simpleMatch(arg: Any) = arg match { case v: Int => "This is an Int" case v: (Int, String) => ("This is a (Int, String): " + v._1 + "," + v._2) case _ => ("Unknown type, print as is: " + _) //模糊匹配，匹配所有的情况，类似* } def caseClassMatch(arg: Any) = arg match { case Dog(_) => arg case Cat(_) => arg case Horse(n, a, w) => w } def constantMatch(arg: Any) = arg match { case 3 => "This is an Int 3" case "3" => "This is a string 3" case true => "This is boolean true" case Nil => "This is a Nil" case null => "This is null" } def partialMatch(arg: List[_]) = arg match { case List(0, _, _) => "This is a list of length 3, and also starts with 0" case List(0, _*) => "This is a list of length not 3, and starts with 0: " + arg.size } def tupleMatch(arg: Any) = arg match { case (k, v) => "Tuple2: " + k + "," + v case (k, v, w) => "Tuple3: " + k + "," + v + "," + w } def typeMatch(arg: Any) = arg match { case v: Int => "Int:" + v case m: Map[_, _] => "Map:" + m.size case t: (_, _) => "Tuple2: " + t._1 + "," + t._2 case _ => "Unknown type:" + arg } def typeEraseMatch(arg: Any) = arg match { case m: Map[Int, Int] => "Map from Int to Int:" + m.size case l: List[Int] => "Int List: " + l.size case t: (String, String) => "String tuple" + t._1 } def arrayTypeEraseMatch(arg: Any) = arg match { case ia: Array[Int] => "Int Array: " + ia.length case sa: Array[String] => "String List: " + sa.length } def precedenceMatch(arg: Any) = arg match { case e: IllegalArgumentException => "This is an IllegalArgumentException" case e: Exception => "This is an Exception." } def optionMatch(arg: Option[_]) = arg match { case Some(s) => s case None => "?" } //等同于 abstract class Animal { /*empty body*/} abstract class Animal //1. 无参的case class已经deprecated //2. name默认成为case class的val field //3. 无需new Cat("kitty") //4.可以copy进行构造一个全新的case class，只有部分属性不同的情况很合适 //5. match/case匹配，match/case class匹配,=>用于分隔模式和模式匹配结果的表达式 //6. match/case匹配，match/case class匹配,case中的属性值，可以使用变量指代或者_指代 //7. case _ => expr，表达的是模糊匹配或者任意匹配 //8.常量匹配 //9. List匹配 //10. Tuple匹配 //11.类型匹配 //12. 集合元素的类型运行时擦除：List,Map,Tuple，不包括数组 //13. 数组元素类型运行时不檫除 //14.匹配优先级，类似switch/case+break //15. Option case class Cat(name: String) extends Animal case class Dog(name: String) extends Animal case class Horse(name: String, age: Int, weight: Double) def main(args: Array[String]) { println(Cat("kitty")) println(Cat("kitty").name) println(new Dog("carl")) val h1 = Horse("H", 8, 121.1) val h2 = h1.copy(name = "X") println(h2) println(simpleMatch(100)) println(simpleMatch(100, "200")) println(caseClassMatch(Dog("Carl"))) println(caseClassMatch(Horse("H", 11, 222.2))) //常量匹配 println(constantMatch(3)) println(constantMatch(1 == 1)) println(constantMatch("3")) println(constantMatch(null)) println(constantMatch(Nil)) //Nil表示空List //部分匹配 println(partialMatch(List(0, 1, 2))) println(partialMatch(List(0, 1, 2, 3))) //元组匹配 println(tupleMatch(1, 2)) println(tupleMatch("One", "Tow", "Three")) //类型匹配 println(typeMatch(100)) println(typeMatch(Map(1 -> 2, 2 -> 3))) println(typeMatch(("One", "Two"))) println(typeMatch(("One", "Two", "Three"))) //Unknown type //类型的运行时擦除：List,Map,Tuple println(typeEraseMatch(Map(1 -> 1, 2 -> 2))) //匹配m成功 println(typeEraseMatch(Map("One" -> "One", "Two" -> "Two"))) //匹配m成功 println(typeEraseMatch(List(1, 2, 3))) //匹配l成功 println(typeEraseMatch(List("One", "Two", "Three"))) //匹配l成功 println(typeEraseMatch((1, 1))) //匹配t成功 println(typeEraseMatch(("One", "One"))) //匹配t成功 println(arrayTypeEraseMatch(Array(1, 2))) //匹配ia成功 println(arrayTypeEraseMatch(Array("One", "Two"))) //匹配sa成功 println(precedenceMatch(new IllegalArgumentException())) println(precedenceMatch(new NullPointerException())) //Option匹配 println(optionMatch(Map("One"->"Two").get("One"))) //Two println(optionMatch(Map("One"->"Two").get("1"))) //? }}
A case class is a simple type of immutable class that comes with implementations of all of the basic Java class methods, like toString, equals, and hashCode, which makes them very easy to use
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