[SCALA-26] First draft

Author: artem.kupchinskiy

core-scala/src/main/scala/com/baeldung/scala/equality/package.scala

@@ -0,0 +1,22 @@
+package com.baeldung.scala
+
+package object equality {
+
+  // A class with default equals/hashcode implementations
+  class PersonFirst(val name: String, val age: Int)
+
+  // A class with overridden equals/hashcode implementations
+  class PersonSecond(val name: String, val age: Int) {
+    override def equals(other: Any): Boolean = other match {
+      case person: PersonSecond =>
+        this.name == person.name && this.age == person.age
+      case _ => false
+    }
+
+    override def hashCode(): Int = if (name eq null) age else name.hashCode + 31 * age
+  }
+
+  // A case class with the compiler-generated equals/hashcode implementations
+  case class PersonThird(name: String, age: Int)
+
+}

core-scala/src/test/scala/com/baeldung/scala/equality/EqualityTest.scala

@@ -0,0 +1,59 @@
+package com.baeldung.scala.equality
+
+import org.scalatest.FlatSpec
+
+class EqualityTest extends FlatSpec {
+  "Equality operator for AnyVal" should "work as in Java" in {
+    val intAnyVal = 4
+    val booleanAnyVal = false
+    assert(intAnyVal == 2 * 2)
+    assert((intAnyVal > 10) == booleanAnyVal)
+  }
+
+  "Equality operator for referential types" should "work like null-safe equals()" in {
+    val str1 = new String("AnyRef")
+    val str2 = new String("AnyRef")
+    val str3 = null
+    val str4 = null
+    assert(str1 == str2)
+    // Unlike in java, the following lines of code do not cause NullPointerExceptions
+    assert(str3 != str2)
+    assert(str4 == str3)
+  }
+
+  "Equals()" should "work as in Java" in {
+    val str1 = new String("AnyRef")
+    val str2 = new String("AnyRef")
+    val str3 = null
+    assert(str1.equals(str2))
+    assertThrows[NullPointerException](str3.equals(str2))
+  }
+
+  "Eq and ne" should "check referential equality" in {
+    val str1 = new String("AnyRef")
+    val str2 = new String("AnyRef")
+    val str3 = str2
+    assert(str1 ne str2)
+    assert(str3 eq str2)
+    // Both operators are null-safe
+    assert(null eq null)
+    assert(null ne str1)
+  }
+
+  "Equality operator" should "not work out of the box for PersonFirst" in {
+    val pf1 = new PersonFirst("Donald", 66)
+    val pf2 = new PersonFirst("Donald", 66)
+    assert(pf1 != pf2)
+  }
+
+  "Equality operator" should "work for PersonSecond and PersonThird" in {
+    val ps1 = new PersonSecond("Donald", 66)
+    val ps2 = new PersonSecond("Donald", 66)
+    val pt1 = PersonThird("Donald", 66)
+    val pt2 = PersonThird("Donald", 66)
+    assert(ps1 == ps2)
+    assert(pt1 == pt2)
+    // There is no duck-typing though
+    assert(ps1 != pt1)
+  }
+}