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@nenono nenono/Comparing.scala
Last active Aug 29, 2015

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Scalaでオブジェクトの比較(等値性、同一性、大小)
// オブジェクトの比較
object Comparing {
// ---------------------------------------------------------------------------------
// 適当なcase class
case class SomeCase(key1:Int, key2:String)
// 適当なclass
class SomeClass(val key1:Int, val key2:String)
def equalsTest = {
println("equalsTest")
// 以下全てtrue
println(1 == 1)
println(1 != 2)
println(true == true)
println(null == null)
// 文字列も値比較
println("aaaaa" == "aaaaa")
// ケースクラスも値比較
println(SomeCase(1, "a") == SomeCase(1, "a"))
println(SomeCase(1, "a") != SomeCase(1, "b"))
// Tuple
println((1, 2) == (1, 2))
// List
println(List(1, 2, 3) == List(1, 2, 3))
// Vector
println(Vector(1, 2, 3) == Vector(1, 2, 3))
// Map
println(Map("a"->1, "b"->2) == Map("a"->1, "b"->2))
// Set
println(Set(1, 2, 3) == Set(3, 2, 1))
// 通常のオブジェクトでは参照比較になります
println(new SomeClass(1, "a") != new SomeClass(1, "a"))
// ポインタ比較をしたい場合は eq/ne演算子を使います
val x = new SomeClass(1, "a")
println(x eq x)
println(null ne x)
// 配列も参照比較
println(Array(1, 2, 3) != Array(1, 2, 3))
println(Array(1, 2, 3).sameElements(Array(1, 2, 3))) // 要素比較の場合はsameElementsメソッドを使います
}
// ---------------------------------------------------------------------------------
// ==演算子でequalsメソッドが呼ばれる確認
class SomeClass2(val key:Int) {
override def equals(other: Any) = {
println("equals called!")
other match {
case that: SomeClass2 => key == that.key // 型の一致でパターンマッチ
case _ => false
}
}
}
def equalsTest2 = {
println("--equalsTest2--")
println(null == new SomeClass2(1)) // false
println(null != new SomeClass2(1)) // true
println(new SomeClass2(1) == new SomeClass2(1)) // equalsが呼び出されて、true
println(new SomeClass2(1) != new SomeClass2(2)) // equalsが呼び出されて、true
}
// ---------------------------------------------------------------------------------
// 大小比較
// 参考: [Scala - 大小比較の可能なcase class - Qiita](http://qiita.com/edvakf@github/items/01572c97bee954905a01)
case class Row(age:Int, name:String) extends Ordered[Row]{
override def compare(other: Row): Int = Ordering.by(Row.unapply).compare(this, other)
}
def lessMoreTest = {
println("--lessMoreTest--")
val rows = Vector(Row(19, "bob"), Row(19, "alice"), Row(17, "charlie"))
println(rows.sorted) // charlie, alice, bob
}
def main(args: Array[String]) {
equalsTest
equalsTest2
lessMoreTest
}
}
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