Implement ValueObject.sameValueAs(), and use that as delegate in equals()

dddsample/src/main/java/se/citerus/dddsample/domain/TrackingId.java

@@ -5,11 +5,10 @@ import org.apache.commons.lang.builder.EqualsBuilder;
 import org.apache.commons.lang.builder.HashCodeBuilder;
 
 /**
- * Identifies a particular cargo.
- * <p/>
- * Make sure to put a constraint in the database to make sure TrackingId is unique.
+ * Uniquely identifies a particular cargo. Automatically generated by the application.
+ *  
  */
-public final class TrackingId {
+public final class TrackingId implements ValueObject<TrackingId> {
 
   private String id;
 
@@ -31,8 +30,13 @@ public final class TrackingId {
   }
 
   @Override
-  public boolean equals(final Object obj) {
-    return EqualsBuilder.reflectionEquals(this, obj);
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+
+    TrackingId other = (TrackingId) o;
+
+    return sameValueAs(other);
   }
 
   @Override
@@ -40,9 +44,11 @@ public final class TrackingId {
     return HashCodeBuilder.reflectionHashCode(this);
   }
 
+  public boolean sameValueAs(TrackingId other) {
+    return other != null && EqualsBuilder.reflectionEquals(this, other);
+  }
 
   TrackingId() {
     // Needed by Hibernate
   }
-
 }