utility method to calculate average time between entries

src/main/java/com/commafeed/backend/feeds/FeedUtils.java

@@ -1,12 +1,17 @@
 package com.commafeed.backend.feeds;
 
+import java.util.List;
+
 import org.apache.commons.lang.StringUtils;
+import org.apache.commons.math.stat.descriptive.SummaryStatistics;
 import org.jsoup.Jsoup;
 import org.jsoup.nodes.Document.OutputSettings;
 import org.jsoup.nodes.Entities.EscapeMode;
 import org.jsoup.safety.Whitelist;
 import org.mozilla.universalchardet.UniversalDetector;
 
+import com.commafeed.backend.model.FeedEntry;
+
 public class FeedUtils {
 
 	public static String guessEncoding(byte[] bytes) {
@@ -95,4 +100,14 @@ public class FeedUtils {
 		}
 		return sb.toString();
 	}
+
+	public static long average(List<FeedEntry> entries) {
+		SummaryStatistics stats = new SummaryStatistics();
+		for (int i = 0; i < entries.size() - 1; i++) {
+			long diff = Math.abs(entries.get(i).getUpdated().getTime()
+					- entries.get(i + 1).getUpdated().getTime());
+			stats.addValue(diff);
+		}
+		return (long) stats.getMean();
+	}
 }

src/main/java/com/commafeed/backend/feeds/FetchedFeed.java

@@ -1,7 +1,7 @@
 package com.commafeed.backend.feeds;
 
-import java.util.Collection;
 import java.util.Date;
+import java.util.List;
 
 import com.commafeed.backend.model.Feed;
 import com.commafeed.backend.model.FeedEntry;
@@ -10,7 +10,7 @@ import com.google.api.client.util.Lists;
 public class FetchedFeed {
 
 	private Feed feed = new Feed();
-	private Collection<FeedEntry> entries = Lists.newArrayList();
+	private List<FeedEntry> entries = Lists.newArrayList();
 
 	private String title;
 	private long fetchDuration;
@@ -24,11 +24,11 @@ public class FetchedFeed {
 		this.feed = feed;
 	}
 
-	public Collection<FeedEntry> getEntries() {
+	public List<FeedEntry> getEntries() {
 		return entries;
 	}
 
-	public void setEntries(Collection<FeedEntry> entries) {
+	public void setEntries(List<FeedEntry> entries) {
 		this.entries = entries;
 	}