diff --git a/src/main/java/envoy/data/Contact.java b/src/main/java/envoy/data/Contact.java
index 3e830f1..96b703e 100644
--- a/src/main/java/envoy/data/Contact.java
+++ b/src/main/java/envoy/data/Contact.java
@@ -15,7 +15,7 @@ import java.io.Serializable;
  */
 public abstract class Contact implements Serializable {
 
-	private long	id;
+	private final long	id;
 	private String	name;
 
 	private static final long serialVersionUID = 0L;
diff --git a/src/main/java/envoy/data/Group.java b/src/main/java/envoy/data/Group.java
index 7de0f20..cab866f 100644
--- a/src/main/java/envoy/data/Group.java
+++ b/src/main/java/envoy/data/Group.java
@@ -2,6 +2,7 @@ package envoy.data;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.StringJoiner;
 
 /**
  * Project: <strong>envoy-common</strong><br>
@@ -57,12 +58,10 @@ public class Group extends Contact {
 	 */
 	@Override
 	public String toString() {
-		StringBuilder sb = new StringBuilder();
-		sb.append("Group[id=" + getId() + ",name=" + getName() + ",memberIDs=[");
-		memberIDs.forEach(id -> { sb.append(id); sb.append(", "); });
-		// deleting the final ", "
-		sb.delete(sb.length() - 2, sb.length());
-		sb.append("]]");
-		return sb.toString();
+		var joiner = new StringJoiner(",", "Group[id=", "]");
+		joiner.add("id=" + getId());
+		joiner.add("name=" + getName());
+		joiner.add("memberIDs=" + getMemberIDs());
+		return joiner.toString();
 	}
 }