第16章：Scalaの等価性 ref: http://qiita.com/f81@github/items/a90c16419645be5d7008

CaseClass.scala

object CaseClass {

  def main(args: Array[String]): Unit = {
    val domain1 = new Domain3(1, "富樫")
    val domain2 = new Domain3(1, "富樫")

    println("==:", domain1 == domain2)
    println("!=:", domain1 != domain2)

    val domain3 = new Domain3(2, "虎丸")

    println("==:", domain1 == domain3)
    println("!=:", domain1 != domain3)

  }

  case class Domain3(val id: Long, val name: String)
}

Equals.java

public class Equals {
    public static void main(String[] args) {
        final String a = new String("test");
        final String b = new String("test");

        System.out.println(a == b);
        System.out.println(a.equals(b));
    }
}

Equivalence.scala

object Equivalence {

  def main(args: Array[String]): Unit = {
    val domain1 = new Domain1(1, "富樫")
    val domain2 = new Domain1(1, "富樫")

    println(domain1 == domain2)
    println(domain1 != domain2)

    val domain3 = new Domain1(2, "虎丸")

    println("==:", domain1 == domain3)
    println("!=:", domain1 != domain3)
  }

}

class Domain1(val id: Long, val name: String) {
  def canEqual(other: Any) = {
    other.isInstanceOf[Domain1]
  }

  override def equals(other: Any) = {
    other match {
      case that: Domain1 =>
        that.canEqual(Domain1.this) && id == that.id && name == that.name
      case _ => false
    }
  }

  override def hashCode() = {
    val prime = 41
    prime * (prime + id.hashCode) + name.hashCode
  }
}

file1.scala

$ scala Equivalence
true   // domain1 == domain2
false  // domain1 != domain2
false  // domain1 == domain3
true   // domain1 != domain3

file3.scala

$ scala Identity
true   // domain1 eq domain2
false  // domain1 ne domain2
false  // domain1 eq domain3
true   // domain1 ne domain3

file5.java

false  // a == b
true   // a.equals(b)

file7.scala

scala CaseClass
true   // domain1 == domain2
false  // domain1 != domain2
false  // domain1 == domain3
true   // domain1 != domain3

file9.scala

$ scala NoneCaseClass
true   // domain1 == domain2
false  // domain1 != domain2
false  // domain1 == domain3
true   // domain1 != domain3

Identity.scala

object Identity {

  def main(args: Array[String]): Unit = {
    val domain1 = new Domain2(1, "富樫")
    val domain2 = domain1

    println(domain1 eq domain2)
    println(domain1 ne domain2)

    val domain3 = new Domain2(1, "富樫")

    println(domain1 eq domain3)
    println(domain1 ne domain3)
  }

}

class Domain2(val id: Long, val name: String) {
  def canEqual(other: Any) = {
    other.isInstanceOf[Domain2]
  }

  override def equals(other: Any) = {
    other match {
      case that: Domain2 =>
        that.canEqual(Domain2.this) && id == that.id && name == that.name
      case _ => false
    }
  }

  override def hashCode() = {
    val prime = 41
    prime * (prime + id.hashCode) + name.hashCode
  }
}

NoneCaseClass.scala

object NoneCaseClass {

  def main(args: Array[String]): Unit = {
    val domain1 = new Domain4(1, "富樫")
    val domain2 = domain1

    println("==:", domain1 == domain2)
    println("!=:", domain1 != domain2)

    val domain3 = new Domain4(2, "虎丸")

    println("==:", domain1 == domain3)
    println("!=:", domain1 != domain3)

  }

  class Domain4(val id: Long, val name: String)
}