diff --git a/ultrasonic/src/main/java/org/moire/ultrasonic/util/LRUCache.java b/ultrasonic/src/main/java/org/moire/ultrasonic/util/LRUCache.java
deleted file mode 100644
index 2adc7cea..00000000
--- a/ultrasonic/src/main/java/org/moire/ultrasonic/util/LRUCache.java
+++ /dev/null
@@ -1,117 +0,0 @@
-/*
- This file is part of Subsonic.
-
- Subsonic is free software: you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation, either version 3 of the License, or
- (at your option) any later version.
-
- Subsonic is distributed in the hope that it will be useful,
- but WITHOUT ANY WARRANTY; without even the implied warranty of
- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- GNU General Public License for more details.
-
- You should have received a copy of the GNU General Public License
- along with Subsonic.  If not, see <http://www.gnu.org/licenses/>.
-
- Copyright 2009 (C) Sindre Mehus
- */
-package org.moire.ultrasonic.util;
-
-import java.lang.ref.SoftReference;
-import java.util.HashMap;
-import java.util.Map;
-
-/**
- * @author Sindre Mehus
- */
-public class LRUCache<K, V>
-{
-
-	private final int capacity;
-	private final Map<K, TimestampedValue> map;
-
-	public LRUCache(int capacity)
-	{
-		map = new HashMap<K, TimestampedValue>(capacity);
-		this.capacity = capacity;
-	}
-
-	public synchronized V get(K key)
-	{
-		TimestampedValue value = map.get(key);
-
-		V result = null;
-		if (value != null)
-		{
-			value.updateTimestamp();
-			result = value.getValue();
-		}
-
-		return result;
-	}
-
-	public synchronized void put(K key, V value)
-	{
-		if (map.size() >= capacity)
-		{
-			removeOldest();
-		}
-		map.put(key, new TimestampedValue(value));
-	}
-
-	public void clear()
-	{
-		map.clear();
-	}
-
-	private void removeOldest()
-	{
-		K oldestKey = null;
-		long oldestTimestamp = Long.MAX_VALUE;
-
-		for (Map.Entry<K, TimestampedValue> entry : map.entrySet())
-		{
-			K key = entry.getKey();
-			TimestampedValue value = entry.getValue();
-			if (value.getTimestamp() < oldestTimestamp)
-			{
-				oldestTimestamp = value.getTimestamp();
-				oldestKey = key;
-			}
-		}
-
-		if (oldestKey != null)
-		{
-			map.remove(oldestKey);
-		}
-	}
-
-	private final class TimestampedValue
-	{
-
-		private final SoftReference<V> value;
-		private long timestamp;
-
-		public TimestampedValue(V value)
-		{
-			this.value = new SoftReference<V>(value);
-			updateTimestamp();
-		}
-
-		public V getValue()
-		{
-			return value.get();
-		}
-
-		public long getTimestamp()
-		{
-			return timestamp;
-		}
-
-		public void updateTimestamp()
-		{
-			timestamp = System.currentTimeMillis();
-		}
-	}
-}
\ No newline at end of file
diff --git a/ultrasonic/src/main/kotlin/org/moire/ultrasonic/util/LRUCache.kt b/ultrasonic/src/main/kotlin/org/moire/ultrasonic/util/LRUCache.kt
new file mode 100644
index 00000000..22ab7f60
--- /dev/null
+++ b/ultrasonic/src/main/kotlin/org/moire/ultrasonic/util/LRUCache.kt
@@ -0,0 +1,79 @@
+/*
+ * LRUCache.kt
+ * Copyright (C) 2009-2021 Ultrasonic developers
+ *
+ * Distributed under terms of the GNU GPLv3 license.
+ */
+package org.moire.ultrasonic.util
+
+import java.lang.ref.SoftReference
+import java.util.HashMap
+
+/**
+ * A cache that deletes the least-recently-used items.
+ */
+class LRUCache<K, V>(capacity: Int) {
+    private val capacity: Int
+    private val map: MutableMap<K, TimestampedValue>
+
+    @Synchronized
+    operator fun get(key: K): V? {
+        val value = map[key]
+        var result: V? = null
+        if (value != null) {
+            value.updateTimestamp()
+            result = value.getValue()
+        }
+        return result
+    }
+
+    @Synchronized
+    fun put(key: K, value: V) {
+        if (map.size >= capacity) {
+            removeOldest()
+        }
+        map[key] = TimestampedValue(value)
+    }
+
+    fun clear() {
+        map.clear()
+    }
+
+    private fun removeOldest() {
+        var oldestKey: K? = null
+        var oldestTimestamp = Long.MAX_VALUE
+        for ((key, value) in map) {
+            if (value.timestamp < oldestTimestamp) {
+                oldestTimestamp = value.timestamp
+                oldestKey = key
+            }
+        }
+        if (oldestKey != null) {
+            map.remove(oldestKey)
+        }
+    }
+
+    private inner class TimestampedValue(value: V) {
+        private val value: SoftReference<V> = SoftReference(value)
+
+        var timestamp: Long = 0
+            private set
+
+        fun getValue(): V? {
+            return value.get()
+        }
+
+        fun updateTimestamp() {
+            timestamp = System.currentTimeMillis()
+        }
+
+        init {
+            updateTimestamp()
+        }
+    }
+
+    init {
+        map = HashMap(capacity)
+        this.capacity = capacity
+    }
+}