update Identifiable

mllib/src/main/scala/org/apache/spark/ml/util/Identifiable.scala

@@ -19,15 +19,31 @@ package org.apache.spark.ml.util
 
 import java.util.UUID
 
+
 /**
- * Object with a unique id.
+ * Object with a unique ID that identifies itself and its derivatives.
  */
 private[ml] trait Identifiable extends Serializable {
 
   /**
-   * A unique id for the object. The default implementation concatenates the class name, "_", and 8
-   * random hex chars.
+   * A unique ID for the object and its derivatives. The default implementation concatenates
+   * [[simpleClassName]], "_", and 8 random hex chars.
+   */
+  final def uid: String = _uid
+
+  /**
+   * A simple name of the class, which is used as the first part of the generated UID. The default
+   * implementation uses [[java.lang.Class#getSimpleName()]].
    */
-  private[ml] val uid: String =
-    this.getClass.getSimpleName + "_" + UUID.randomUUID().toString.take(8)
+  protected def simpleClassName: String = this.getClass.getSimpleName
+
+  /**
+   * Sets the UID of the instance.
+   */
+  protected final def setUID(uid: String): this.type = {
+    this._uid = uid
+    this
+  }
+
+  private var _uid = simpleClassName + "_" + UUID.randomUUID().toString.take(8)
 }

mllib/src/test/java/org/apache/spark/ml/util/IdentifiableSuite.scala

@@ -0,0 +1,50 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.util
+
+import org.scalatest.FunSuite
+
+class IdentifiableSuite extends FunSuite {
+
+  import IdentifiableSuite._
+
+  test("Identifiable") {
+    val test0 = new Test0
+    assert(test0.uid.startsWith(classOf[Test0].getSimpleName + "_"))
+
+    val test1 = new Test1
+    assert(test1.uid.startsWith("test_"),
+      "simpleClassName should be the first part of the generated UID.")
+    val copied = test1.copy
+    assert(copied.uid === test1.uid, "Copied objects should be able to use the same UID.")
+  }
+}
+
+object IdentifiableSuite {
+
+  class Test0 extends Identifiable
+
+  class Test1 extends Identifiable {
+
+    override def simpleClassName: String = "test"
+
+    def copy: Test1 = {
+      new Test1().setUID(uid)
+    }
+  }
+}