Improve LinkedHashMap Java compatibility

- make it a subclass of `HashMap` ((accidentally?) relied upon by a Guava test)
- make `HashMap` non-final (add one more bridge method so overrides will work as
  intended)
- make `LinkedHashMap` non-final
- add `LinkedHashMap#clone`

PiperOrigin-RevId: 610402905

Author: martinkretzschmar

j2kt/jre/java/common/java/util/HashMap.java

@@ -20,15 +20,13 @@
 import org.jspecify.nullness.NullMarked;
 import org.jspecify.nullness.Nullable;
 
-// TODO(b/240106068): Native HashMap is final. But this class should be non-final.
-// We need to add bridges for java_get etc. before it is safe to remove final.
 /**
  * See <a href="https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html">the official Java
  * API doc</a> for details.
  */
 @KtNative(name = "java.util.HashMap")
 @NullMarked
-public final class HashMap<K extends @Nullable Object, V extends @Nullable Object>
+public class HashMap<K extends @Nullable Object, V extends @Nullable Object>
     extends AbstractMap<K, V> implements Cloneable, Serializable {
 
   public HashMap() {}

j2kt/jre/java/common/java/util/LinkedHashMap.java

@@ -64,7 +64,9 @@ open class HashMap<K, V> private constructor(val ktHashMap: KotlinHashMap<K, V>)
 
   @Suppress("UNCHECKED_CAST") override fun java_remove(key: Any?): V? = ktHashMap.remove(key as K)
 
-  override fun putAll(m: KotlinMap<out K, V>) = ktHashMap.putAll(m)
+  override fun java_putAll(m: MutableMap<out K, out V>) = ktHashMap.putAll(m)
+
+  override fun putAll(m: KotlinMap<out K, V>) = java_putAll(m as MutableMap<out K, out V>)
 
   override fun clear() = ktHashMap.clear()
 

j2kt/jre/java/native/java/util/HashMap.kt

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2008 Google Inc.
+ *
+ * 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 java.util;
+
+import org.jspecify.nullness.NullMarked;
+import org.jspecify.nullness.Nullable;
+
+// Note: This implementation relies on the fact that Kotlin Native's HashMap is linked.
+/**
+ * See <a href="https://docs.oracle.com/javase/8/docs/api/java/util/LinkedHashMap.html">the official
+ * Java API doc</a> for details.
+ */
+@NullMarked
+public class LinkedHashMap<K extends @Nullable Object, V extends @Nullable Object>
+    extends HashMap<K, V> implements Map<K, V>, Cloneable {
+
+  public LinkedHashMap() {
+    super();
+  }
+
+  public LinkedHashMap(int initialCapacity) {
+    super(initialCapacity);
+  }
+
+  public LinkedHashMap(int initialCapacity, float loadFactor) {
+    super(initialCapacity, loadFactor);
+  }
+
+  public LinkedHashMap(Map<? extends K, ? extends V> original) {
+    super(original);
+  }
+
+  @Override
+  public Object clone() {
+    return new LinkedHashMap<K, V>(this);
+  }
+}