diff --git a/app/src/main/java/protect/card_locker/BarcodeImageWriterResultCallback.java b/app/src/main/java/protect/card_locker/BarcodeImageWriterResultCallback.java
deleted file mode 100644
index a2616459e..000000000
--- a/app/src/main/java/protect/card_locker/BarcodeImageWriterResultCallback.java
+++ /dev/null
@@ -1,5 +0,0 @@
-package protect.card_locker;
-
-public interface BarcodeImageWriterResultCallback {
-    void onBarcodeImageWriterResult(boolean success);
-}
diff --git a/app/src/main/java/protect/card_locker/BarcodeImageWriterResultCallback.kt b/app/src/main/java/protect/card_locker/BarcodeImageWriterResultCallback.kt
new file mode 100644
index 000000000..f81b438dc
--- /dev/null
+++ b/app/src/main/java/protect/card_locker/BarcodeImageWriterResultCallback.kt
@@ -0,0 +1,5 @@
+package protect.card_locker
+
+interface BarcodeImageWriterResultCallback {
+    fun onBarcodeImageWriterResult(success: Boolean)
+}
diff --git a/app/src/main/java/protect/card_locker/async/CompatCallable.java b/app/src/main/java/protect/card_locker/async/CompatCallable.java
deleted file mode 100644
index 352e0aeac..000000000
--- a/app/src/main/java/protect/card_locker/async/CompatCallable.java
+++ /dev/null
@@ -1,9 +0,0 @@
-package protect.card_locker.async;
-
-import java.util.concurrent.Callable;
-
-public interface CompatCallable<T> extends Callable<T> {
-    void onPostExecute(Object result);
-
-    void onPreExecute();
-}
diff --git a/app/src/main/java/protect/card_locker/async/CompatCallable.kt b/app/src/main/java/protect/card_locker/async/CompatCallable.kt
new file mode 100644
index 000000000..38763c1bb
--- /dev/null
+++ b/app/src/main/java/protect/card_locker/async/CompatCallable.kt
@@ -0,0 +1,9 @@
+package protect.card_locker.async
+
+import java.util.concurrent.Callable
+
+interface CompatCallable<T> : Callable<T?> {
+    fun onPostExecute(result: Any?)
+
+    fun onPreExecute()
+}
diff --git a/app/src/main/java/protect/card_locker/importexport/DataFormat.java b/app/src/main/java/protect/card_locker/importexport/DataFormat.java
deleted file mode 100644
index 929d7c236..000000000
--- a/app/src/main/java/protect/card_locker/importexport/DataFormat.java
+++ /dev/null
@@ -1,7 +0,0 @@
-package protect.card_locker.importexport;
-
-public enum DataFormat {
-    Catima,
-    Fidme,
-    VoucherVault;
-}
diff --git a/app/src/main/java/protect/card_locker/importexport/DataFormat.kt b/app/src/main/java/protect/card_locker/importexport/DataFormat.kt
new file mode 100644
index 000000000..ae87a25ef
--- /dev/null
+++ b/app/src/main/java/protect/card_locker/importexport/DataFormat.kt
@@ -0,0 +1,7 @@
+package protect.card_locker.importexport
+
+enum class DataFormat {
+    Catima,
+    Fidme,
+    VoucherVault
+}
diff --git a/app/src/main/java/protect/card_locker/importexport/Exporter.java b/app/src/main/java/protect/card_locker/importexport/Exporter.java
deleted file mode 100644
index c6af80c88..000000000
--- a/app/src/main/java/protect/card_locker/importexport/Exporter.java
+++ /dev/null
@@ -1,20 +0,0 @@
-package protect.card_locker.importexport;
-
-import android.content.Context;
-import android.database.sqlite.SQLiteDatabase;
-
-import java.io.IOException;
-import java.io.OutputStream;
-
-/**
- * Interface for a class which can export the contents of the database
- * in a given format.
- */
-public interface Exporter {
-    /**
-     * Export the database to the output stream in a given format.
-     *
-     * @throws IOException
-     */
-    void exportData(Context context, SQLiteDatabase database, OutputStream output, char[] password) throws IOException, InterruptedException;
-}
diff --git a/app/src/main/java/protect/card_locker/importexport/Exporter.kt b/app/src/main/java/protect/card_locker/importexport/Exporter.kt
new file mode 100644
index 000000000..bc407248b
--- /dev/null
+++ b/app/src/main/java/protect/card_locker/importexport/Exporter.kt
@@ -0,0 +1,25 @@
+package protect.card_locker.importexport
+
+import android.content.Context
+import android.database.sqlite.SQLiteDatabase
+import java.io.IOException
+import java.io.OutputStream
+
+/**
+ * Interface for a class which can export the contents of the database
+ * in a given format.
+ */
+interface Exporter {
+    /**
+     * Export the database to the output stream in a given format.
+     *
+     * @throws IOException, InterruptedException
+     */
+    @Throws(IOException::class, InterruptedException::class)
+    fun exportData(
+        context: Context,
+        database: SQLiteDatabase,
+        output: OutputStream,
+        password: CharArray
+    )
+}
diff --git a/app/src/main/java/protect/card_locker/importexport/ImportExportResultType.java b/app/src/main/java/protect/card_locker/importexport/ImportExportResultType.java
deleted file mode 100644
index 940488b1a..000000000
--- a/app/src/main/java/protect/card_locker/importexport/ImportExportResultType.java
+++ /dev/null
@@ -1,7 +0,0 @@
-package protect.card_locker.importexport;
-
-public enum ImportExportResultType {
-    Success,
-    GenericFailure,
-    BadPassword;
-}
\ No newline at end of file
diff --git a/app/src/main/java/protect/card_locker/importexport/ImportExportResultType.kt b/app/src/main/java/protect/card_locker/importexport/ImportExportResultType.kt
new file mode 100644
index 000000000..6f5a57580
--- /dev/null
+++ b/app/src/main/java/protect/card_locker/importexport/ImportExportResultType.kt
@@ -0,0 +1,7 @@
+package protect.card_locker.importexport
+
+enum class ImportExportResultType {
+    Success,
+    GenericFailure,
+    BadPassword
+}
\ No newline at end of file
diff --git a/app/src/main/java/protect/card_locker/importexport/Importer.java b/app/src/main/java/protect/card_locker/importexport/Importer.java
deleted file mode 100644
index 72c32d377..000000000
--- a/app/src/main/java/protect/card_locker/importexport/Importer.java
+++ /dev/null
@@ -1,27 +0,0 @@
-package protect.card_locker.importexport;
-
-import android.content.Context;
-import android.database.sqlite.SQLiteDatabase;
-
-import org.json.JSONException;
-
-import java.io.File;
-import java.io.IOException;
-import java.text.ParseException;
-
-import protect.card_locker.FormatException;
-
-/**
- * Interface for a class which can import the contents of a stream
- * into the database.
- */
-public interface Importer {
-    /**
-     * Import data from the input stream in a given format into
-     * the database.
-     *
-     * @throws IOException
-     * @throws FormatException
-     */
-    void importData(Context context, SQLiteDatabase database, File inputFile, char[] password) throws IOException, FormatException, InterruptedException, JSONException, ParseException;
-}
diff --git a/app/src/main/java/protect/card_locker/importexport/Importer.kt b/app/src/main/java/protect/card_locker/importexport/Importer.kt
new file mode 100644
index 000000000..599a3f46d
--- /dev/null
+++ b/app/src/main/java/protect/card_locker/importexport/Importer.kt
@@ -0,0 +1,39 @@
+package protect.card_locker.importexport
+
+import android.content.Context
+import android.database.sqlite.SQLiteDatabase
+import org.json.JSONException
+import protect.card_locker.FormatException
+import java.io.File
+import java.io.IOException
+import java.text.ParseException
+
+/**
+ * Interface for a class which can import the contents of a stream
+ * into the database.
+ */
+interface Importer {
+    /**
+     * Import data from the input stream in a given format into
+     * the database.
+     *
+     * @throws IOException
+     * @throws FormatException
+     * @throws InterruptedException
+     * @throws JSONException
+     * @throws ParseException
+     */
+    @Throws(
+        IOException::class,
+        FormatException::class,
+        InterruptedException::class,
+        JSONException::class,
+        ParseException::class
+    )
+    fun importData(
+        context: Context,
+        database: SQLiteDatabase,
+        inputFile: File,
+        password: CharArray
+    )
+}