Return more specific types (e.g. Collection → List)

be generic as possible in what you accept, but more specific in what you
return.

Also tweak MultiuserChatManager methods a bit.

smack-core/src/main/java/org/jivesoftware/smack/Chat.java

@@ -21,7 +21,6 @@ import org.jivesoftware.smack.SmackException.NotConnectedException;
 import org.jivesoftware.smack.packet.Message;
 
 import java.util.Set;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.concurrent.CopyOnWriteArraySet;
 
@@ -141,12 +140,12 @@ public class Chat {
     }
 
     /**
-     * Returns an unmodifiable collection of all of the listeners registered with this chat.
+     * Returns an unmodifiable set of all of the listeners registered with this chat.
      *
-     * @return an unmodifiable collection of all of the listeners registered with this chat.
+     * @return an unmodifiable set of all of the listeners registered with this chat.
      */
-    public Collection<ChatMessageListener> getListeners() {
-        return Collections.unmodifiableCollection(listeners);
+    public Set<ChatMessageListener> getListeners() {
+        return Collections.unmodifiableSet(listeners);
     }
 
     /**

smack-core/src/main/java/org/jivesoftware/smack/ChatManager.java

@@ -17,7 +17,6 @@
 
 package org.jivesoftware.smack;
 
-import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
@@ -322,14 +321,14 @@ public class ChatManager extends Manager{
     }
 
     /**
-     * Returns an unmodifiable collection of all chat listeners currently registered with this
+     * Returns an unmodifiable set of all chat listeners currently registered with this
      * manager.
      *
      * @return an unmodifiable collection of all chat listeners currently registered with this
      * manager.
      */
-    public Collection<ChatManagerListener> getChatListeners() {
-        return Collections.unmodifiableCollection(chatManagerListeners);
+    public Set<ChatManagerListener> getChatListeners() {
+        return Collections.unmodifiableSet(chatManagerListeners);
     }
 
     private void deliverMessage(Chat chat, Message message) {

smack-core/src/main/java/org/jivesoftware/smack/Roster.java

@@ -369,12 +369,12 @@ public class Roster {
     }
 
     /**
-     * Returns an unmodifiable collection of all entries in the roster, including entries
+     * Returns a set of all entries in the roster, including entries
      * that don't belong to any groups.
      *
      * @return all entries in the roster.
      */
-    public Collection<RosterEntry> getEntries() {
+    public Set<RosterEntry> getEntries() {
         Set<RosterEntry> allEntries = new HashSet<RosterEntry>();
         // Loop through all roster groups and add their entries to the answer
         for (RosterGroup rosterGroup : getGroups()) {
@@ -383,7 +383,7 @@ public class Roster {
         // Add the roster unfiled entries to the answer
         allEntries.addAll(unfiledEntries);
 
-        return Collections.unmodifiableCollection(allEntries);
+        return allEntries;
     }
 
     /**
@@ -402,7 +402,7 @@ public class Roster {
      *
      * @return the unfiled roster entries.
      */
-    public Collection<RosterEntry> getUnfiledEntries() {
+    public List<RosterEntry> getUnfiledEntries() {
         return Collections.unmodifiableList(unfiledEntries);
     }
 

smack-core/src/main/java/org/jivesoftware/smack/RosterEntry.java

@@ -19,7 +19,6 @@ package org.jivesoftware.smack;
 
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 
@@ -112,11 +111,11 @@ public class RosterEntry {
     }
 
     /**
-     * Returns an unmodifiable collection of the roster groups that this entry belongs to.
+     * Returns an copied list of the roster groups that this entry belongs to.
      *
      * @return an iterator for the groups this entry belongs to.
      */
-    public Collection<RosterGroup> getGroups() {
+    public List<RosterGroup> getGroups() {
         List<RosterGroup> results = new ArrayList<RosterGroup>();
         // Loop through all roster groups and find the ones that contain this
         // entry. This algorithm should be fine
@@ -125,7 +124,7 @@ public class RosterEntry {
                 results.add(group);
             }
         }
-        return Collections.unmodifiableCollection(results);
+        return results;
     }
 
     /**

smack-core/src/main/java/org/jivesoftware/smack/RosterGroup.java

@@ -18,9 +18,8 @@
 package org.jivesoftware.smack;
 
 import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Locale;
 import java.util.Set;
 
@@ -99,13 +98,13 @@ public class RosterGroup {
     }
 
     /**
-     * Returns an unmodifiable collection of all entries in the group.
+     * Returns an copied list of all entries in the group.
      *
      * @return all entries in the group.
      */
-    public Collection<RosterEntry> getEntries() {
+    public List<RosterEntry> getEntries() {
         synchronized (entries) {
-            return Collections.unmodifiableList(new ArrayList<RosterEntry>(entries));
+            return new ArrayList<RosterEntry>(entries);
         }
     }
 

smack-core/src/main/java/org/jivesoftware/smack/packet/Message.java

@@ -18,7 +18,6 @@
 package org.jivesoftware.smack.packet;
 
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.List;
@@ -154,8 +153,8 @@ public final class Message extends Packet {
      *
      * @return a collection of all subjects in this message.
      */
-    public Collection<Subject> getSubjects() {
-        return Collections.unmodifiableCollection(subjects);
+    public Set<Subject> getSubjects() {
+        return Collections.unmodifiableSet(subjects);
     }
 
     /**
@@ -218,7 +217,7 @@ public final class Message extends Packet {
      *
      * @return the languages being used for the subjects.
      */
-    public Collection<String> getSubjectLanguages() {
+    public List<String> getSubjectLanguages() {
         Subject defaultSubject = getMessageSubject(null);
         List<String> languages = new ArrayList<String>();
         for (Subject subject : subjects) {
@@ -226,7 +225,7 @@ public final class Message extends Packet {
                 languages.add(subject.language);
             }
         }
-        return Collections.unmodifiableCollection(languages);
+        return Collections.unmodifiableList(languages);
     }
 
     /**
@@ -274,8 +273,8 @@ public final class Message extends Packet {
      * @return a collection of all bodies in this Message.
      * @since 3.0.2
      */
-    public Collection<Body> getBodies() {
-        return Collections.unmodifiableCollection(bodies);
+    public Set<Body> getBodies() {
+        return Collections.unmodifiableSet(bodies);
     }
 
     /**
@@ -340,7 +339,7 @@ public final class Message extends Packet {
      * @return the languages being used for the bodies.
      * @since 3.0.2
      */
-    public Collection<String> getBodyLanguages() {
+    public List<String> getBodyLanguages() {
         Body defaultBody = getMessageBody(null);
         List<String> languages = new ArrayList<String>();
         for (Body body : bodies) {
@@ -348,7 +347,7 @@ public final class Message extends Packet {
                 languages.add(body.language);
             }
         }
-        return Collections.unmodifiableCollection(languages);
+        return Collections.unmodifiableList(languages);
     }
 
     /**

smack-core/src/main/java/org/jivesoftware/smack/packet/RosterPacket.java

@@ -20,7 +20,6 @@ package org.jivesoftware.smack.packet;
 import org.jivesoftware.smack.util.XmlStringBuilder;
 
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 import java.util.Locale;
@@ -67,13 +66,13 @@ public class RosterPacket extends IQ {
     }
 
     /**
-     * Returns an unmodifiable collection for the roster items in the packet.
+     * Returns a copied list of the roster items in the packet.
      *
-     * @return an unmodifiable collection for the roster items in the packet.
+     * @return a copied list of the roster items in the packet.
      */
-    public Collection<Item> getRosterItems() {
+    public List<Item> getRosterItems() {
         synchronized (rosterItems) {
-            return Collections.unmodifiableList(new ArrayList<Item>(rosterItems));
+            return new ArrayList<Item>(rosterItems);
         }
     }