make CacheKey comparable

The CacheKey is used as a key in a HashMap. Lookup can
be faster if the CacheKey is comparable when there are
hash collisions.
In this case I was not able to measure any effect. I am
keeping the comparables nonetheless, because the can
only have a positive effect.

pdb-api/src/main/java/org/lucares/pdb/api/Tag.java

@@ -1,6 +1,6 @@
 package org.lucares.pdb.api;
 
-public class Tag {
+public class Tag implements Comparable<Tag> {
 	private final int key;
 
 	private final int value;
@@ -15,6 +15,18 @@ public class Tag {
 		this.value = Tags.STRING_COMPRESSOR.put(value);
 	}
 
+	@Override
+	public int compareTo(final Tag o) {
+
+		if (key != o.key) {
+			return key - o.key;
+		} else if (value != o.value) {
+			return value - o.value;
+		}
+
+		return 0;
+	}
+
 	public int getKey() {
 		return key;
 	}

pdb-api/src/main/java/org/lucares/pdb/api/Tags.java

@@ -11,7 +11,7 @@ import java.util.function.Function;
 import org.lucares.collections.LongList;
 import org.lucares.utils.byteencoder.VariableByteEncoder;
 
-public class Tags {
+public class Tags implements Comparable<Tags> {
 
 	public static StringCompressor STRING_COMPRESSOR = null;
 	private static final byte[] EMPTY_BYTES = new byte[0];
@@ -109,6 +109,23 @@ public class Tags {
 		return result;
 	}
 
+	@Override
+	public int compareTo(final Tags o) {
+
+		if (tags.size() != o.tags.size()) {
+			return tags.size() - o.tags.size();
+		} else {
+			for (int i = 0; i < tags.size(); i++) {
+				final int compareResult = tags.get(i).compareTo(o.tags.get(i));
+				if (compareResult != 0) {
+					return compareResult;
+				}
+			}
+		}
+
+		return 0;
+	}
+
 	public String getValue(final String key) {
 		final Tag needle = new Tag(STRING_COMPRESSOR.put(key), 0);