在前面章節裏,咱們瞭解了 class ,object的區別,簡單回顧下程序員
calss 靜態模板(理解成傳統的class就能夠)app
object 單例類,對object作點補充ide
1. 既然是單例,就不能被new,如object名爲SharkObj不能寫成spa
//var so = new SharkObj //error var so = SharkObj //正確
2. 能夠直接寫類名調用方法,假設SharkObj有方法m(x:Int)scala
SharkObj.m(1)
那case classes 又是作什麼的呢? 你能夠就把他理解成一個普通的class,可是又略有不一樣,總結以下:繼承
不須要寫 new, 可是能夠寫ci
默認是public ,在任何地方調用get
默認實現了toStringhash
不能被繼承it
對case calss的質疑聲音比較高,感受價值不大。官方原文:
It makes only sense to define case classes if pattern matching is used to decompose data structures.
固然,只有在pattern matching下有意義這話未免有所偏激,至少部分老程序員會有其餘意見:
get auto-generated equals, hashCode, toString, static apply() for shorter initialization, etc.
這裏簡單表示下,理解爲 match case的控制語句
下面把官方例子貼給你們:
abstract class Term case class Var(name: String) extends Term case class Var1 extends Term case class Fun(arg: String, body: Term) extends Term case class App(f: Term, v: Term) extends Term object TermTest extends scala.App { def printTerm(term: Term) { term match { case Var(n) => print(n) case Fun(x1, b) => print("^" + x1 + ".") printTerm(b) case App(f, v) => print("(") printTerm(f) print(" ") printTerm(v) print(")") } } def isIdentityFun(term: Term): Boolean = term match { case Fun(x, Var(y)) if x == y => true case _ => false } val id = Fun("x", Var("x")) val t = Fun("x", Fun("y", App(Var("x"), Var("y")))) printTerm(t) println println(isIdentityFun(id)) println(isIdentityFun(t)) println(new Var1==new Var1); println(new Var("")==new Var("1")); }