#3 -- fix comparator

src/main/java/ru/ulstu/db/model/TimeSeriesMeta.java

@@ -2,7 +2,7 @@ package ru.ulstu.db.model;
 
 import ru.ulstu.datamodel.ts.TimeSeries;
 
-public class TimeSeriesMeta {
+public class TimeSeriesMeta implements Comparable<TimeSeriesMeta> {
     private String key;
     private int size;
     private boolean hasDateTime;
@@ -31,4 +31,9 @@ public class TimeSeriesMeta {
     public boolean isHasDateTime() {
         return hasDateTime;
     }
+
+    @Override
+    public int compareTo(TimeSeriesMeta o) {
+        return o != null ? key.compareTo(o.getKey()) : 0;
+    }
 }

src/main/java/ru/ulstu/db/model/TimeSeriesSet.java

@@ -2,7 +2,7 @@ package ru.ulstu.db.model;
 
 import java.io.File;
 
-public class TimeSeriesSet {
+public class TimeSeriesSet implements Comparable<TimeSeriesSet> {
     private final String key;
 
     public TimeSeriesSet(File dir) {
@@ -16,4 +16,9 @@ public class TimeSeriesSet {
     public String getKey() {
         return key;
     }
+
+    @Override
+    public int compareTo(TimeSeriesSet o) {
+        return o != null ? key.compareTo(o.getKey()) : 0;
+    }
 }