Migrate class NamedItem to Kotlin.

src/test/java/de/mrapp/apriori/NamedItem.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2017 - 2018 Michael Rapp
+ *
+ * Licensed 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 de.mrapp.apriori
+
+import de.mrapp.util.Condition
+
+/**
+ * An implementation of the type [Item], which is used for test purposes. Each item can
+ * unambiguously be identified via its name.
+ *
+ * @property name The name of the item
+ * @author Michael Rapp
+ */
+data class NamedItem(val name: String) : Item {
+
+    init {
+        Condition.ensureNotEmpty(name, "The name may not be empty")
+    }
+
+    override fun compareTo(other: Item) = toString().compareTo(other.toString())
+
+    override fun toString() = name
+
+    override fun hashCode(): Int {
+        val prime = 31
+        var result = 1
+        result = prime * result + name.hashCode()
+        return result
+    }
+
+    override fun equals(other: Any?): Boolean {
+        if (this === other)
+            return true
+        if (other == null)
+            return false
+        if (javaClass != other.javaClass)
+            return false
+        val another = other as NamedItem
+        return name == another.name
+    }
+
+}