altoslib: Make AltosPreferencesBackend abstract. Add set/put Serializable

This lets us add functionality to this directly, such as the new
serializable APIs.

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/altoslib/AltosFrequency.java b/altoslib/AltosFrequency.java
index 80e0d724..9542fe33 100644
--- a/altoslib/AltosFrequency.java
+++ b/altoslib/AltosFrequency.java
@@ -17,7 +17,11 @@
 
 package org.altusmetrum.altoslib_10;
 
-public class AltosFrequency {
+import java.io.*;
+import java.util.*;
+import java.text.*;
+
+public class AltosFrequency implements Serializable {
 	public double	frequency;
 	public String	description;