diff --git a/src/main/java/eirb/pg203/weather/data/api/WeatherDataCache.java b/src/main/java/eirb/pg203/weather/data/api/WeatherDataCache.java
index 23309c8..88381b7 100644
--- a/src/main/java/eirb/pg203/weather/data/api/WeatherDataCache.java
+++ b/src/main/java/eirb/pg203/weather/data/api/WeatherDataCache.java
@@ -12,9 +12,9 @@ import org.json.JSONObject;
 
 public class WeatherDataCache {
   private static class CacheValue {
-    private WeatherData value;
-    private int day;
-    private Instant timestamp;
+    private final WeatherData value;
+    private final int day;
+    private final Instant timestamp;
 
     CacheValue(WeatherData value, int day, Instant timestamp) {
       this.value = value;
@@ -61,7 +61,7 @@ public class WeatherDataCache {
   }
 
   private HashMap<String, CacheValue> cache = new HashMap<>();
-  private long cacheTTL = 3600;  // Cache data Time To Live in sec
+  private static final long cacheTTL = 3600;  // Cache data Time To Live in sec
 
 	private String makeKey(String cityName, int day) {
 		return String.format(Locale.ENGLISH, "%s%d", cityName, day);
@@ -87,7 +87,7 @@ public class WeatherDataCache {
 
     long dt = Instant.now().getEpochSecond() - cacheValue.getTimestamp().getEpochSecond();
 
-    return dt > this.cacheTTL;  // if older than TTL, needs update
+    return dt > cacheTTL;  // if older than TTL, needs update
   }
 
 	/*