Add buildable for java.util.HashMap

core/shared/src/main/scala-2.12-/org/scalacheck/util/BuildableVersionSpecific.scala

@@ -9,13 +9,19 @@
 
 package org.scalacheck.util
 
-import java.util.ArrayList
+import java.util.{ArrayList, HashMap}
 
 import collection.{Map => _, _}
 import generic.CanBuildFrom
 import scala.collection.mutable.Builder
 
 private[util] trait BuildableVersionSpecific {
+  import scala.collection.JavaConverters._
+  import scala.language.implicitConversions
+
+  implicit def wrapArrayList[T](xs: ArrayList[T]): Traversable[T] = xs.asScala
+  implicit def wrapHashMap[K, V](xs: HashMap[K, V]): Traversable[(K, V)] = xs.asScala
+
   implicit def buildableCanBuildFrom[T, F, C](implicit c: CanBuildFrom[F, T, C]): Buildable[T, C] =
     new Buildable[T, C] {
       def builder = c.apply
@@ -32,6 +38,18 @@ private[util] class ArrayListBuilder[T] extends Builder[T, ArrayList[T]] {
   def result(): ArrayList[T] = al
 }
 
+private[util] class HashMapBuilder[K, V] extends Builder[(K, V), HashMap[K, V]] {
+  private val hm = new HashMap[K, V]
+
+  def +=(x: (K, V)): this.type = {
+    val (k, v) = x
+    hm.put(k, v)
+    this
+  }
+  def clear(): Unit = hm.clear()
+  def result(): HashMap[K, V] = hm
+}
+
 /** CanBuildFrom instances implementing Serializable, so that the objects capturing those can be serializable too.
   */
 object SerializableCanBuildFroms {

core/shared/src/main/scala-2.13+/org/scalacheck/util/BuildableVersionSpecific.scala

@@ -9,11 +9,16 @@
 
 package org.scalacheck.util
 
-import java.util.ArrayList
+import java.util.{ArrayList, HashMap}
 import scala.collection.mutable.Builder
 import scala.collection.{Map => _, _}
 
 private[util] trait BuildableVersionSpecific {
+  import scala.jdk.CollectionConverters._
+
+  implicit def wrapArrayList[T](xs: ArrayList[T]): Iterable[T] = xs.asScala
+  implicit def wrapHashMap[K, V](xs: HashMap[K, V]): Iterable[(K, V)] = xs.asScala
+
   implicit def buildableFactory[T, C](implicit f: Factory[T, C]): Buildable[T, C] =
     new Buildable[T, C] {
       def builder = f.newBuilder
@@ -30,6 +35,17 @@ private[util] class ArrayListBuilder[T] extends Builder[T, ArrayList[T]] {
   def result(): ArrayList[T] = al
 }
 
+private[util] class HashMapBuilder[K, V] extends Builder[(K, V), HashMap[K, V]] {
+  private val hm = new HashMap[K, V]
+  def addOne(x: (K, V)): this.type = {
+    val (k, v) = x
+    hm.put(k, v)
+    this
+  }
+  def clear(): Unit = hm.clear()
+  def result(): HashMap[K, V] = hm
+}
+
 /** Factory instances implementing Serializable, so that the objects capturing those can be serializable too.
   */
 // Named `...CanBuildFroms` for 2.12 source compatibility (`import SerializableCanBuildFroms._`)

core/shared/src/main/scala/org/scalacheck/util/Buildable.scala

@@ -22,12 +22,18 @@ trait Buildable[T, C] extends Serializable {
 }
 
 object Buildable extends BuildableVersionSpecific {
-  import java.util.ArrayList
+  import java.util.{ArrayList, HashMap}
+
   implicit def buildableArrayList[T]: Buildable[T, ArrayList[T]] =
     new Buildable[T, ArrayList[T]] {
       def builder = new ArrayListBuilder[T]
     }
 
+  implicit def buildableHashMap[K, V]: Buildable[(K, V), HashMap[K, V]] =
+    new Buildable[(K, V), HashMap[K, V]] {
+      def builder = new HashMapBuilder[K, V]
+    }
+
   def buildableSeq[T]: Buildable[T, Seq[T]] =
     new Buildable[T, Seq[T]] {
       def builder: mutable.Builder[T, Seq[T]] =

core/shared/src/test/scala/org/scalacheck/util/BuildableSpecification.scala

@@ -12,6 +12,7 @@ package util
 
 import scala.collection._
 
+import Buildable._
 import ScalaVersionSpecific._
 
 object BuildableSpecification {
@@ -47,4 +48,15 @@ object BuildableSpecification {
   implicit val iterableGen: Gen[immutable.Iterable[String]] = container[immutable.Iterable]
 
   implicit val trieIteratorGen: Gen[immutable.Queue[String]] = container[immutable.Queue]
+
+  implicit val arrayListGen: Gen[java.util.ArrayList[String]] = container[java.util.ArrayList]
+
+  def buildable[C[_, _]](implicit
+      evb: Buildable[(String, Long), C[String, Long]],
+      evt: C[String, Long] => Traversable[(String, Long)]
+  ) = Gen.buildableOf[C[String, Long], (String, Long)](for (str <- Gen.alphaStr; lng <- Gen.long) yield (str, lng))
+
+  implicit val mapGen: Gen[Map[String, Long]] = buildable[Map]
+
+  implicit val hashMapGen: Gen[java.util.HashMap[String, Long]] = buildable[java.util.HashMap]
 }