Fix issues found by FindBugs: EQ_COMPARETO_USE_OBJECT_EQUALS

http://findbugs.sourceforge.net/bugDescriptions.html#EQ_COMPARETO_USE_OBJECT_EQUALS

* For each Comparable class that has compareTo() method, add
  the corresponding equals() and hashCode() methods.
* Added/updated some of the Javadoc for the compareTo() methods
* Added a TODO comment inside class ControllerRegistryEntry

Change-Id: Idda67721329a21227c2136a4a2b8ee3367e520bc
diff --git a/src/main/java/net/onrc/onos/core/registry/ControllerRegistryEntry.java b/src/main/java/net/onrc/onos/core/registry/ControllerRegistryEntry.java
index 7e13fdd..569a922 100644
--- a/src/main/java/net/onrc/onos/core/registry/ControllerRegistryEntry.java
+++ b/src/main/java/net/onrc/onos/core/registry/ControllerRegistryEntry.java
@@ -4,7 +4,11 @@
 
 
 public class ControllerRegistryEntry implements Comparable<ControllerRegistryEntry> {
-
+    //
+    // TODO: Refactor the implementation and decide whether controllerId
+    // is needed. If "yes", we might need to consider it inside the
+    // compareTo(), equals() and hashCode() impmenetations.
+    //
     private String controllerId;
     private int sequenceNumber;
 
@@ -18,10 +22,47 @@
         return controllerId;
     }
 
+    /**
+     * Compares this object with the specified object for order.
+     * NOTE: the test is based on ControllerRegistryEntry sequence numbers,
+     * and doesn't include the controllerId.
+     *
+     * @param o the object to be compared.
+     * @return a negative integer, zero, or a positive integer as this object
+     * is less than, equal to, or greater than the specified object.
+     */
     @Override
     public int compareTo(ControllerRegistryEntry o) {
-        return sequenceNumber - o.sequenceNumber;
-        //return 0;
+        return this.sequenceNumber - o.sequenceNumber;
     }
 
+    /**
+     * Test whether some other object is "equal to" this one.
+     * NOTE: the test is based on ControllerRegistryEntry sequence numbers,
+     * and doesn't include the controllerId.
+     *
+     * @param obj the reference object with which to compare.
+     * @return true if this object is the same as the obj argument; false
+     * otherwise.
+     */
+    @Override
+    public boolean equals(Object obj) {
+        if (obj instanceof ControllerRegistryEntry) {
+            ControllerRegistryEntry other = (ControllerRegistryEntry) obj;
+            return this.sequenceNumber == other.sequenceNumber;
+        }
+        return false;
+    }
+
+    /**
+     * Get the hash code for the object.
+     * NOTE: the computation is based on ControllerRegistryEntry sequence
+     * numbers, and doesn't include the controller ID.
+     *
+     * @return a hash code value for this object.
+     */
+    @Override
+    public int hashCode() {
+        return Integer.valueOf(this.sequenceNumber).hashCode();
+    }
 }