case class,样例类,有人也叫条件类。
例如:
case class Person(name:String, age:Int)
好用之处:
1.新建类实例不用new Person(..),直接用Person("qh",20)
2.自动定义好getXX方法,Person("qh",20).name // "qh"
3.提供默认的toString(), Person("qh",20) // "Person(qh,20)"
4.用case class代替tuple
val p = ("qh",20) // p._1 = "qh", p._2 = 20;好处是简洁,但无意义 case class person(name:String, age:Int) val p = person("qh",20) // p.name = "qh", p.age = 20; 好处是有名字,自说明,可读性强
5.经过优化用于模式匹配
def main(args: Array[String]): Unit = {
val alice = Person("Alice", 25)
val bob = Person("Bob", 32)
val charlie = Person("Charlie", 32) for (person <- List(alice, bob, charlie)) {
person match {
case Person("Alice", 25) => println("Hi Alice!")
case Person("Bob", 32) => println("Hi Bob!")
case Person(name, age) =>
println("Age: " + age + " year, name: " + name + "?")
}
}
}
输出结果为:
Hi Alice!
Hi Bob!
Age: 32 year, name: Charlie?
总结:
在定义一些大家约定的规范时,最好用case class,比如spark rdd转化为dataframe时,一个常用的办法就是通过case class