Add checkstyle rule for StringBuilder.append(char)

And replace all instances where String.Builder.append() is called with a
String of length one with append(char).

Also adds StringUtils.toStringBuilder(Collection, String).

config/checkstyle.xml

@@ -19,6 +19,18 @@
 		<property name="format" value="MXParser"/>
 		<property name="message" value="Must not use MXParser, use XmlPullParserFactory instead"/>
 	</module>
+	<module name="RegexpSingleline">
+	  <!--
+		  Matches StringBuilder.append(String) calls where the
+		  argument is a String of length one. Those should be replaced
+		  with append(char) for performance reasons.
+
+		  TODO: This could be more advanced in order to match also
+		  - .append("\u1234")
+	  -->
+		<property name="format" value="\.append\(&quot;(.|\\.)&quot;\)"/>
+		<property name="message" value="Don&apos;t use StringBuilder.append(String) when you can use StringBuilder.append(char). Solution: Replace double quotes of append&apos;s argument with single quotes."/>
+	</module>
 	<module name="RegexpSingleline">
 		<property name="format" value="^\s+$"/>
 		<property name="message" value="Line containing only whitespace character(s)"/>

smack-core/src/integration-test/java/org/jivesoftware/smack/MessageTest.java

@@ -160,7 +160,7 @@ public class MessageTest extends SmackTestCase {
         Message msg = new Message(getFullJID(1), Message.Type.chat);
         StringBuilder sb = new StringBuilder(5000);
         for (int i = 0; i <= 4000; i++) {
-            sb.append("X");
+            sb.append('X');
         }
         msg.setBody(sb.toString());
 

smack-core/src/main/java/org/jivesoftware/smack/filter/AbstractListFilter.java

@@ -19,10 +19,10 @@ package org.jivesoftware.smack.filter;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.Iterator;
 import java.util.List;
 
 import org.jivesoftware.smack.util.Objects;
+import org.jivesoftware.smack.util.StringUtils;
 
 public abstract class AbstractListFilter implements StanzaFilter {
 
@@ -67,14 +67,8 @@ public abstract class AbstractListFilter implements StanzaFilter {
         StringBuilder sb = new StringBuilder();
         sb.append(getClass().getSimpleName());
         sb.append(": (");
-        for (Iterator<StanzaFilter> it = filters.iterator(); it.hasNext();) {
+        sb.append(StringUtils.toStringBuilder(filters, ", "));
-            StanzaFilter filter = it.next();
+        sb.append(')');
-            sb.append(filter.toString());
-            if (it.hasNext()) {
-                sb.append(", ");
-            }
-        }
-        sb.append(")");
         return sb.toString();
     }
 }

smack-core/src/main/java/org/jivesoftware/smack/util/StringUtils.java

@@ -222,21 +222,32 @@ public class StringUtils {
     }
 
     /**
-     * Transform a collection of CharSequences to a whitespace delimited String.
+     * Transform a collection of objects to a whitespace delimited String.
      *
      * @param collection the collection to transform.
      * @return a String with all the elements of the collection.
      */
-    public static String collectionToString(Collection<? extends CharSequence> collection) {
+    public static String collectionToString(Collection<? extends Object> collection) {
+        return toStringBuilder(collection, " ").toString();
+    }
+
+    /**
+     * Transform a collection of objects to a delimited String.
+     *
+     * @param collection the collection to transform.
+     * @param delimiter the delimiter used to delimit the Strings.
+     * @return a StringBuilder with all the elements of the collection.
+     */
+    public static StringBuilder toStringBuilder(Collection<? extends Object> collection, String delimiter) {
         StringBuilder sb = new StringBuilder(collection.size() * 20);
-        for (Iterator<? extends CharSequence> it = collection.iterator(); it.hasNext();) {
+        for (Iterator<? extends Object> it = collection.iterator(); it.hasNext();) {
-            CharSequence cs = it.next();
+            Object cs = it.next();
             sb.append(cs);
             if (it.hasNext()) {
-                sb.append(' ');
+                sb.append(delimiter);
             }
         }
-        return sb.toString();
+        return sb;
     }
 
     public static String returnIfNotEmptyTrimmed(String string) {

smack-extensions/src/main/java/org/jivesoftware/smackx/address/packet/MultipleAddresses.java

@@ -201,7 +201,7 @@ public class MultipleAddresses implements ExtensionElement {
             buf.optAttribute("desc", description);
             if (description != null && description.trim().length() > 0) {
                 buf.append(" desc=\"");
-                buf.append(description).append("\"");
+                buf.append(description).append('"');
             }
             buf.optBooleanAttribute("delivered", delivered);
             buf.optAttribute("uri", uri);

smack-extensions/src/main/java/org/jivesoftware/smackx/amp/packet/AMPExtension.java

@@ -155,27 +155,27 @@ public class AMPExtension implements ExtensionElement {
     @Override
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" xmlns=\"").append(getNamespace()).append("\"");
+        buf.append('<').append(getElementName()).append(" xmlns=\"").append(getNamespace()).append('"');
         if (status != null) {
-            buf.append(" status=\"").append(status.toString()).append("\"");
+            buf.append(" status=\"").append(status.toString()).append('"');
         }
         if (to != null) {
-            buf.append(" to=\"").append(to).append("\"");
+            buf.append(" to=\"").append(to).append('"');
         }
         if (from != null) {
-            buf.append(" from=\"").append(from).append("\"");
+            buf.append(" from=\"").append(from).append('"');
         }
         if (perHop) {
             buf.append(" per-hop=\"true\"");
         }
-        buf.append(">");
+        buf.append('>');
 
         // Loop through all the rules and append them to the string buffer
         for (Rule rule : getRules()) {
             buf.append(rule.toXML());
         }
 
-        buf.append("</").append(getElementName()).append(">");
+        buf.append("</").append(getElementName()).append('>');
         return buf.toString();
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/attention/packet/AttentionExtension.java

@@ -67,7 +67,7 @@ public class AttentionExtension implements ExtensionElement {
      */
     public String toXML() {
         final StringBuilder sb = new StringBuilder();
-        sb.append("<").append(getElementName()).append(" xmlns=\"").append(
+        sb.append('<').append(getElementName()).append(" xmlns=\"").append(
                 getNamespace()).append("\"/>");
         return sb.toString();
     }

smack-extensions/src/main/java/org/jivesoftware/smackx/caps/EntityCapsManager.java

@@ -631,13 +631,13 @@ public final class EntityCapsManager extends Manager {
         // followed by the '<' character.
         for (DiscoverInfo.Identity identity : sortedIdentities) {
             sb.append(identity.getCategory());
-            sb.append("/");
+            sb.append('/');
             sb.append(identity.getType());
-            sb.append("/");
+            sb.append('/');
             sb.append(identity.getLanguage() == null ? "" : identity.getLanguage());
-            sb.append("/");
+            sb.append('/');
             sb.append(identity.getName() == null ? "" : identity.getName());
-            sb.append("<");
+            sb.append('<');
         }
 
         // 4. Sort the supported service discovery features.
@@ -649,7 +649,7 @@ public final class EntityCapsManager extends Manager {
         // character
         for (String f : features) {
             sb.append(f);
-            sb.append("<");
+            sb.append('<');
         }
 
         // only use the data form for calculation is it has a hidden FORM_TYPE
@@ -690,7 +690,7 @@ public final class EntityCapsManager extends Manager {
                 // followed by the '<' character.
                 for (FormField f : fs) {
                     sb.append(f.getVariable());
-                    sb.append("<");
+                    sb.append('<');
                     formFieldValuesToCaps(f.getValues(), sb);
                 }
             }
@@ -719,7 +719,7 @@ public final class EntityCapsManager extends Manager {
         }
         for (String fv : fvs) {
             sb.append(fv);
-            sb.append("<");
+            sb.append('<');
         }
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/commands/packet/AdHocCommandData.java

@@ -261,7 +261,7 @@ public class AdHocCommandData extends IQ {
 
         public String toXML() {
             StringBuilder buf = new StringBuilder();
-            buf.append("<").append(getElementName());
+            buf.append('<').append(getElementName());
             buf.append(" xmlns=\"").append(getNamespace()).append("\"/>");
             return buf.toString();
         }

smack-extensions/src/main/java/org/jivesoftware/smackx/iqprivate/packet/DefaultPrivateData.java

@@ -81,14 +81,14 @@ public class DefaultPrivateData implements PrivateData {
 
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(elementName).append(" xmlns=\"").append(namespace).append("\">");
+        buf.append('<').append(elementName).append(" xmlns=\"").append(namespace).append("\">");
         for (String name : getNames()) {
             String value = getValue(name);
-            buf.append("<").append(name).append(">");
+            buf.append('<').append(name).append('>');
             buf.append(value);
-            buf.append("</").append(name).append(">");
+            buf.append("</").append(name).append('>');
         }
-        buf.append("</").append(elementName).append(">");
+        buf.append("</").append(elementName).append('>');
         return buf.toString();
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/nick/packet/Nick.java

@@ -86,7 +86,7 @@ public class Nick implements ExtensionElement {
 	public String toXML() {
 		final StringBuilder buf = new StringBuilder();
 
-		buf.append("<").append(ELEMENT_NAME).append(" xmlns=\"").append(
+		buf.append('<').append(ELEMENT_NAME).append(" xmlns=\"").append(
 				NAMESPACE).append("\">");
 		buf.append(getName());
 		buf.append("</").append(ELEMENT_NAME).append('>');

smack-extensions/src/main/java/org/jivesoftware/smackx/offline/packet/OfflineMessageInfo.java

@@ -80,11 +80,11 @@ public class OfflineMessageInfo implements ExtensionElement {
 
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" xmlns=\"").append(getNamespace()).append(
+        buf.append('<').append(getElementName()).append(" xmlns=\"").append(getNamespace()).append(
             "\">");
         if (getNode() != null)
             buf.append("<item node=\"").append(getNode()).append("\"/>");
-        buf.append("</").append(getElementName()).append(">");
+        buf.append("</").append(getElementName()).append('>');
         return buf.toString();
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/offline/packet/OfflineMessageRequest.java

@@ -182,13 +182,13 @@ public class OfflineMessageRequest extends IQ {
             StringBuilder buf = new StringBuilder();
             buf.append("<item");
             if (getAction() != null) {
-                buf.append(" action=\"").append(getAction()).append("\"");
+                buf.append(" action=\"").append(getAction()).append('"');
             }
             if (getJid() != null) {
-                buf.append(" jid=\"").append(getJid()).append("\"");
+                buf.append(" jid=\"").append(getJid()).append('"');
             }
             if (getNode() != null) {
-                buf.append(" node=\"").append(getNode()).append("\"");
+                buf.append(" node=\"").append(getNode()).append('"');
             }
             buf.append("/>");
             return buf.toString();

smack-extensions/src/main/java/org/jivesoftware/smackx/pep/packet/PEPEvent.java

@@ -93,9 +93,9 @@ public class PEPEvent implements ExtensionElement {
      */
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" xmlns=\"").append(getNamespace()).append("\">");
+        buf.append('<').append(getElementName()).append(" xmlns=\"").append(getNamespace()).append("\">");
         buf.append(item.toXML());
-        buf.append("</").append(getElementName()).append(">");
+        buf.append("</").append(getElementName()).append('>');
         return buf.toString();
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/pep/packet/PEPItem.java

@@ -80,9 +80,9 @@ public abstract class PEPItem implements ExtensionElement {
      */
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" id=\"").append(id).append("\">");
+        buf.append('<').append(getElementName()).append(" id=\"").append(id).append("\">");
         buf.append(getItemDetailsXML());
-        buf.append("</").append(getElementName()).append(">");
+        buf.append("</").append(getElementName()).append('>');
         return buf.toString();
     }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/privacy/packet/PrivacyItem.java

@@ -296,17 +296,17 @@ public class PrivacyItem {
         } else {
         	buf.append(" action=\"deny\"");
         }
-        buf.append(" order=\"").append(getOrder()).append("\"");
+        buf.append(" order=\"").append(getOrder()).append('"');
         if (getType() != null) {
-            buf.append(" type=\"").append(getType()).append("\"");
+            buf.append(" type=\"").append(getType()).append('"');
         }
         if (getValue() != null) {
-            buf.append(" value=\"").append(getValue()).append("\"");
+            buf.append(" value=\"").append(getValue()).append('"');
         }
         if (isFilterEverything()) {
         	buf.append("/>");
         } else {
-        	buf.append(">");
+        	buf.append('>');
         	if (this.isFilterIQ()) {
             	buf.append("<iq/>");
             }

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/Item.java

@@ -122,13 +122,13 @@ public class Item extends NodeExtension
 		{
 			builder.append(" id='");
 			builder.append(id);
-			builder.append("'");
+			builder.append('\'');
 		}
 
         if (getNode() != null) {
             builder.append(" node='");
             builder.append(getNode());
-            builder.append("'");
+            builder.append('\'');
         }
 		builder.append("/>");
 

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/ItemsExtension.java

@@ -183,7 +183,7 @@ public class ItemsExtension extends NodeExtension implements EmbeddedPacketExten
 
 			builder.append("</");
 			builder.append(getElementName());
-			builder.append(">");
+			builder.append('>');
 			return builder.toString();
 		}
 	}

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/PayloadItem.java

@@ -118,15 +118,15 @@ public class PayloadItem<E extends ExtensionElement> extends Item
 		{
 			builder.append(" id='");
 			builder.append(getId());
-			builder.append("'");
+			builder.append('\'');
 		}
 
         if (getNode() != null) {
             builder.append(" node='");
             builder.append(getNode());
-            builder.append("'");
+            builder.append('\'');
         }
-		builder.append(">");
+		builder.append('>');
 		builder.append(payload.toXML());
 		builder.append("</item>");
 

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/SubscribeExtension.java

@@ -52,7 +52,7 @@ public class SubscribeExtension extends NodeExtension
 		{
 			builder.append(" node='");
 			builder.append(getNode());
-			builder.append("'");
+			builder.append('\'');
 		}
 		builder.append(" jid='");
 		builder.append(getJid());

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/Subscription.java

@@ -153,11 +153,11 @@ public class Subscription extends NodeExtension
 
 	private static void appendAttribute(StringBuilder builder, String att, String value)
 	{
-		builder.append(" ");
+		builder.append(' ');
 		builder.append(att);
 		builder.append("='");
 		builder.append(value);
-		builder.append("'");
+		builder.append('\'');
 	}
 
 }

smack-extensions/src/main/java/org/jivesoftware/smackx/pubsub/SubscriptionsExtension.java

@@ -81,9 +81,9 @@ public class SubscriptionsExtension extends NodeExtension
 			{
 				builder.append(" node='");
 				builder.append(getNode());
-				builder.append("'");
+				builder.append('\'');
 			}
-			builder.append(">");
+			builder.append('>');
 
 			for (Subscription item : items)
 			{
@@ -92,7 +92,7 @@ public class SubscriptionsExtension extends NodeExtension
 
 			builder.append("</");
 			builder.append(getElementName());
-			builder.append(">");
+			builder.append('>');
 			return builder.toString();
 		}
 	}

smack-extensions/src/main/java/org/jivesoftware/smackx/search/SimpleUserSearch.java

@@ -75,7 +75,7 @@ class SimpleUserSearch extends IQ {
             String name = field.getVariable();
             String value = getSingleValue(field);
             if (value.trim().length() > 0) {
-                buf.append("<").append(name).append(">").append(value).append("</").append(name).append(">");
+                buf.append('<').append(name).append('>').append(value).append("</").append(name).append('>');
             }
         }
 

smack-extensions/src/main/java/org/jivesoftware/smackx/si/packet/StreamInitiation.java

@@ -328,7 +328,7 @@ public class StreamInitiation extends IQ {
         public String toXML() {
             StringBuilder buffer = new StringBuilder();
 
-            buffer.append("<").append(getElementName()).append(" xmlns=\"")
+            buffer.append('<').append(getElementName()).append(" xmlns=\"")
                     .append(getNamespace()).append("\" ");
 
             if (getName() != null) {
@@ -348,14 +348,14 @@ public class StreamInitiation extends IQ {
             }
 
             if ((desc != null && desc.length() > 0) || isRanged) {
-                buffer.append(">");
+                buffer.append('>');
                 if (getDesc() != null && desc.length() > 0) {
                     buffer.append("<desc>").append(StringUtils.escapeForXML(getDesc())).append("</desc>");
                 }
                 if (isRanged()) {
                     buffer.append("<range/>");
                 }
-                buffer.append("</").append(getElementName()).append(">");
+                buffer.append("</").append(getElementName()).append('>');
             }
             else {
                 buffer.append("/>");

smack-extensions/src/main/java/org/jivesoftware/smackx/xdata/Form.java

@@ -376,7 +376,7 @@ public class Form {
             sb.append(it.next());
             // If this is not the last instruction then append a newline
             if (it.hasNext()) {
-                sb.append("\n");
+                sb.append('\n');
             }
         }
         return sb.toString();

smack-im/src/main/java/org/jivesoftware/smack/roster/RosterEntry.java

@@ -207,7 +207,7 @@ public final class RosterEntry extends Manager {
                 group = iter.next();
                 buf.append(group.getName());
             }
-            buf.append("]");
+            buf.append(']');
         }
         return buf.toString();
     }

smack-java7/src/main/java/org/jivesoftware/smack/java7/XmppHostnameVerifier.java

@@ -154,7 +154,7 @@ public class XmppHostnameVerifier implements HostnameVerifier {
                 StringBuilder sb = new StringBuilder("No subject alternative DNS name matching "
                                 + name + " found. Tried: ");
                 for (String nonMatchingDnsAltname : nonMatchingDnsAltnames) {
-                    sb.append(nonMatchingDnsAltname).append(",");
+                    sb.append(nonMatchingDnsAltname).append(',');
                 }
                 throw new CertificateException(sb.toString());
             }
@@ -279,7 +279,7 @@ public class XmppHostnameVerifier implements HostnameVerifier {
         StringBuilder sb = new StringBuilder("No subject alternative names matching IP address "
                         + expectedIP + " found. Tried: ");
         for (String s : nonMatchingIpAltnames) {
-            sb.append(s).append(",");
+            sb.append(s).append(',');
         }
         throw new CertificateException(sb.toString());
     }

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/media/PayloadType.java

@@ -208,17 +208,17 @@ public class PayloadType {
     public String toXML() {
         StringBuilder buf = new StringBuilder();
 
-            buf.append("<").append(getElementName()).append(" ");
+            buf.append('<').append(getElementName()).append(' ');
 
             // We covert here the payload type to XML
             if (this.getId() != PayloadType.INVALID_PT) {
-                buf.append(" id=\"").append(this.getId()).append("\"");
+                buf.append(" id=\"").append(this.getId()).append('"');
             }
             if (this.getName() != null) {
-                buf.append(" name=\"").append(this.getName()).append("\"");
+                buf.append(" name=\"").append(this.getName()).append('"');
             }
             if (this.getChannels() != 0) {
-                buf.append(" channels=\"").append(this.getChannels()).append("\"");
+                buf.append(" channels=\"").append(this.getChannels()).append('"');
             }
             if (getChildAttributes() != null) {
                 buf.append(getChildAttributes());

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/nat/RTPBridge.java

@@ -134,22 +134,22 @@ public class RTPBridge extends IQ {
         StringBuilder str = new StringBuilder();
 
         if (getSid() != null)
-            str.append(" sid='").append(getSid()).append("'");
+            str.append(" sid='").append(getSid()).append('\'');
 
         if (getPass() != null)
-            str.append(" pass='").append(getPass()).append("'");
+            str.append(" pass='").append(getPass()).append('\'');
 
         if (getPortA() != -1)
-            str.append(" porta='").append(getPortA()).append("'");
+            str.append(" porta='").append(getPortA()).append('\'');
 
         if (getPortB() != -1)
-            str.append(" portb='").append(getPortB()).append("'");
+            str.append(" portb='").append(getPortB()).append('\'');
 
         if (getHostA() != null)
-            str.append(" hosta='").append(getHostA()).append("'");
+            str.append(" hosta='").append(getHostA()).append('\'');
 
         if (getHostB() != null)
-            str.append(" hostb='").append(getHostB()).append("'");
+            str.append(" hostb='").append(getHostB()).append('\'');
 
         return str.toString();
     }

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/Jingle.java

@@ -345,18 +345,18 @@ public class Jingle extends IQ {
      */
     protected IQChildElementXmlStringBuilder getIQChildElementBuilder(IQChildElementXmlStringBuilder buf) {
         if (getInitiator() != null) {
-            buf.append(" initiator=\"").append(getInitiator()).append("\"");
+            buf.append(" initiator=\"").append(getInitiator()).append('"');
         }
         if (getResponder() != null) {
-            buf.append(" responder=\"").append(getResponder()).append("\"");
+            buf.append(" responder=\"").append(getResponder()).append('"');
         }
         if (getAction() != null) {
-            buf.append(" action=\"").append(getAction().name()).append("\"");
+            buf.append(" action=\"").append(getAction().name()).append('"');
         }
         if (getSid() != null) {
-            buf.append(" sid=\"").append(getSid()).append("\"");
+            buf.append(" sid=\"").append(getSid()).append('"');
         }
-        buf.append(">");
+        buf.append('>');
 
         synchronized (contents) {
             for (JingleContent content : contents) {

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/JingleContent.java

@@ -162,7 +162,7 @@ public class JingleContent implements ExtensionElement {
 
         synchronized (transports) {
 
-            buf.append("<").append(getElementName());
+            buf.append('<').append(getElementName());
 
             buf.append(" creator='" + creator + "' name='" + name + "'>");
 
@@ -175,7 +175,7 @@ public class JingleContent implements ExtensionElement {
             for (JingleTransport transport : transports) {
                 buf.append(transport.toXML());
             }
-            buf.append("</").append(getElementName()).append(">");
+            buf.append("</").append(getElementName()).append('>');
         }
         return buf.toString();
     }

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/JingleContentDescription.java

@@ -149,7 +149,7 @@ public abstract class JingleContentDescription implements ExtensionElement {
 
         synchronized (payloads) {
             if (payloads.size() > 0) {
-                buf.append("<").append(getElementName());
+                buf.append('<').append(getElementName());
                 buf.append(" xmlns=\"").append(getNamespace()).append("\" >");
 
                 Iterator<JinglePayloadType> pt = payloads.listIterator();
@@ -157,7 +157,7 @@ public abstract class JingleContentDescription implements ExtensionElement {
                     JinglePayloadType pte = pt.next();
                     buf.append(pte.toXML());
                 }
-                buf.append("</").append(getElementName()).append(">");
+                buf.append("</").append(getElementName()).append('>');
             }
         }
 
@@ -251,17 +251,17 @@ public abstract class JingleContentDescription implements ExtensionElement {
             StringBuilder buf = new StringBuilder();
 
             if (payload != null) {
-                buf.append("<").append(getElementName()).append(" ");
+                buf.append('<').append(getElementName()).append(' ');
 
                 // We covert here the payload type to XML
                 if (payload.getId() != PayloadType.INVALID_PT) {
-                    buf.append(" id=\"").append(payload.getId()).append("\"");
+                    buf.append(" id=\"").append(payload.getId()).append('"');
                 }
                 if (payload.getName() != null) {
-                    buf.append(" name=\"").append(payload.getName()).append("\"");
+                    buf.append(" name=\"").append(payload.getName()).append('"');
                 }
                 if (payload.getChannels() != 0) {
-                    buf.append(" channels=\"").append(payload.getChannels()).append("\"");
+                    buf.append(" channels=\"").append(payload.getChannels()).append('"');
                 }
                 if (getChildAttributes() != null) {
                     buf.append(getChildAttributes());

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/JingleContentInfo.java

@@ -82,7 +82,7 @@ public class JingleContentInfo implements ExtensionElement {
 
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" xmlns=\"");
+        buf.append('<').append(getElementName()).append(" xmlns=\"");
         buf.append(getNamespace()).append("\" ");
         buf.append("/>");
         return buf.toString();

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/JingleDescription.java

@@ -156,7 +156,7 @@ public abstract class JingleDescription implements ExtensionElement {
 
         synchronized (payloads) {
             if (payloads.size() > 0) {
-                buf.append("<").append(getElementName());
+                buf.append('<').append(getElementName());
                 buf.append(" xmlns=\"").append(getNamespace()).append("\" >");
 
                 for (PayloadType payloadType : payloads) {
@@ -164,7 +164,7 @@ public abstract class JingleDescription implements ExtensionElement {
                         buf.append(payloadType.toXML());
                     }
                 }
-                buf.append("</").append(getElementName()).append(">");
+                buf.append("</").append(getElementName()).append('>');
             }
         }
 

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/JingleError.java

@@ -77,7 +77,7 @@ public class JingleError implements ExtensionElement {
         StringBuilder buf = new StringBuilder();
         if (message != null) {
             buf.append("<error type=\"cancel\">");
-            buf.append("<").append(message).append(" xmlns=\"").append(NAMESPACE).append(
+            buf.append('<').append(message).append(" xmlns=\"").append(NAMESPACE).append(
                     "\"/>");
             buf.append("</error>");
         }

smack-jingle-old/src/main/java/org/jivesoftware/smackx/jingleold/packet/JingleTransport.java

@@ -151,19 +151,19 @@ public class JingleTransport implements ExtensionElement {
     public String toXML() {
         StringBuilder buf = new StringBuilder();
 
-        buf.append("<").append(getElementName()).append(" xmlns=\"");
+        buf.append('<').append(getElementName()).append(" xmlns=\"");
         buf.append(getNamespace()).append("\" ");
 
         synchronized (candidates) {
             if (getCandidatesCount() > 0) {
-                buf.append(">");
+                buf.append('>');
                 Iterator<JingleTransportCandidate> iter = getCandidates();
 
                 while (iter.hasNext()) {
                     JingleTransportCandidate candidate = iter.next();
                     buf.append(candidate.toXML());
                 }
-                buf.append("</").append(getElementName()).append(">");
+                buf.append("</").append(getElementName()).append('>');
             } else {
                 buf.append("/>");
             }
@@ -251,7 +251,7 @@ public class JingleTransport implements ExtensionElement {
             String childElements = getChildElements();
 
             if (transportCandidate != null && childElements != null) {
-                buf.append("<").append(getElementName()).append(" ");
+                buf.append('<').append(getElementName()).append(' ');
                 buf.append(childElements);
                 buf.append("/>");
             }
@@ -323,18 +323,18 @@ public class JingleTransport implements ExtensionElement {
                     ICECandidate tci = (ICECandidate) transportCandidate;
 
                     // We convert the transportElement candidate to XML here...
-                    buf.append(" generation=\"").append(tci.getGeneration()).append("\"");
+                    buf.append(" generation=\"").append(tci.getGeneration()).append('"');
-                    buf.append(" ip=\"").append(tci.getIp()).append("\"");
+                    buf.append(" ip=\"").append(tci.getIp()).append('"');
-                    buf.append(" port=\"").append(tci.getPort()).append("\"");
+                    buf.append(" port=\"").append(tci.getPort()).append('"');
-                    buf.append(" network=\"").append(tci.getNetwork()).append("\"");
+                    buf.append(" network=\"").append(tci.getNetwork()).append('"');
-                    buf.append(" username=\"").append(tci.getUsername()).append("\"");
+                    buf.append(" username=\"").append(tci.getUsername()).append('"');
-                    buf.append(" password=\"").append(tci.getPassword()).append("\"");
+                    buf.append(" password=\"").append(tci.getPassword()).append('"');
-                    buf.append(" preference=\"").append(tci.getPreference()).append("\"");
+                    buf.append(" preference=\"").append(tci.getPreference()).append('"');
-                    buf.append(" type=\"").append(tci.getType()).append("\"");
+                    buf.append(" type=\"").append(tci.getType()).append('"');
 
                     // Optional elements
                     if (transportCandidate.getName() != null) {
-                        buf.append(" name=\"").append(tci.getName()).append("\"");
+                        buf.append(" name=\"").append(tci.getName()).append('"');
                     }
                 }
 
@@ -408,14 +408,14 @@ public class JingleTransport implements ExtensionElement {
                 if (transportCandidate != null && transportCandidate instanceof TransportCandidate.Fixed) {
                     TransportCandidate.Fixed tcf = (TransportCandidate.Fixed) transportCandidate;
 
-                    buf.append(" generation=\"").append(tcf.getGeneration()).append("\"");
+                    buf.append(" generation=\"").append(tcf.getGeneration()).append('"');
-                    buf.append(" ip=\"").append(tcf.getIp()).append("\"");
+                    buf.append(" ip=\"").append(tcf.getIp()).append('"');
-                    buf.append(" port=\"").append(tcf.getPort()).append("\"");
+                    buf.append(" port=\"").append(tcf.getPort()).append('"');
 
                     // Optional parameters
                     String name = tcf.getName();
                     if (name != null) {
-                        buf.append(" name=\"").append(name).append("\"");
+                        buf.append(" name=\"").append(name).append('"');
                     }
                 }
                 return buf.toString();

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/packet/AgentStatus.java

@@ -91,11 +91,11 @@ public class AgentStatus implements ExtensionElement {
     public String toXML() {
         StringBuilder buf = new StringBuilder();
 
-        buf.append("<").append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\"");
+        buf.append('<').append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append('"');
         if (workgroupJID != null) {
-            buf.append(" jid=\"").append(workgroupJID).append("\"");
+            buf.append(" jid=\"").append(workgroupJID).append('"');
         }
-        buf.append(">");
+        buf.append('>');
         if (maxChats != -1) {
             buf.append("<max-chats>").append(maxChats).append("</max-chats>");
         }
@@ -197,22 +197,22 @@ public class AgentStatus implements ExtensionElement {
 
             buf.append("<chat ");
             if (sessionID != null) {
-                buf.append(" sessionID=\"").append(sessionID).append("\"");
+                buf.append(" sessionID=\"").append(sessionID).append('"');
             }
             if (userID != null) {
-                buf.append(" userID=\"").append(userID).append("\"");
+                buf.append(" userID=\"").append(userID).append('"');
             }
             if (date != null) {
-                buf.append(" startTime=\"").append(UTC_FORMAT.format(date)).append("\"");
+                buf.append(" startTime=\"").append(UTC_FORMAT.format(date)).append('"');
             }
             if (email != null) {
-                buf.append(" email=\"").append(email).append("\"");
+                buf.append(" email=\"").append(email).append('"');
             }
             if (username != null) {
-                buf.append(" username=\"").append(username).append("\"");
+                buf.append(" username=\"").append(username).append('"');
             }
             if (question != null) {
-                buf.append(" question=\"").append(question).append("\"");
+                buf.append(" question=\"").append(question).append('"');
             }
             buf.append("/>");
 

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/packet/QueueDetails.java

@@ -108,7 +108,7 @@ public final class QueueDetails implements ExtensionElement {
 
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\">");
+        buf.append('<').append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\">");
 
         synchronized (users) {
             for (Iterator<QueueUser> i=users.iterator(); i.hasNext(); ) {
@@ -136,7 +136,7 @@ public final class QueueDetails implements ExtensionElement {
                 buf.append("</user>");
             }
         }
-        buf.append("</").append(ELEMENT_NAME).append(">");
+        buf.append("</").append(ELEMENT_NAME).append('>');
         return buf.toString();
     }
 

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/packet/QueueOverview.java

@@ -98,7 +98,7 @@ public class QueueOverview implements ExtensionElement {
 
     public String toXML () {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\">");
+        buf.append('<').append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\">");
 
         if (userCount != -1) {
             buf.append("<count>").append(userCount).append("</count>");
@@ -112,7 +112,7 @@ public class QueueOverview implements ExtensionElement {
         if (status != null) {
             buf.append("<status>").append(status).append("</status>");
         }
-        buf.append("</").append(ELEMENT_NAME).append(">");
+        buf.append("</").append(ELEMENT_NAME).append('>');
 
         return buf.toString();
     }

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/packet/SessionID.java

@@ -57,7 +57,7 @@ public class SessionID implements ExtensionElement {
     public String toXML() {
         StringBuilder buf = new StringBuilder();
 
-        buf.append("<").append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\" ");
+        buf.append('<').append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\" ");
         buf.append("id=\"").append(this.getSessionID());
         buf.append("\"/>");
 

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/packet/UserID.java

@@ -59,7 +59,7 @@ public class UserID implements ExtensionElement {
     public String toXML() {
         StringBuilder buf = new StringBuilder();
 
-        buf.append("<").append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\" ");
+        buf.append('<').append(ELEMENT_NAME).append(" xmlns=\"").append(NAMESPACE).append("\" ");
         buf.append("id=\"").append(this.getUserID());
         buf.append("\"/>");
 

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/packet/WorkgroupInformation.java

@@ -62,7 +62,7 @@ public class WorkgroupInformation implements ExtensionElement {
         StringBuilder buf = new StringBuilder();
 
         buf.append('<').append(ELEMENT_NAME);
-        buf.append(" jid=\"").append(getWorkgroupJID()).append("\"");
+        buf.append(" jid=\"").append(getWorkgroupJID()).append('"');
         buf.append(" xmlns=\"").append(NAMESPACE).append("\" />");
 
         return buf.toString();

smack-legacy/src/main/java/org/jivesoftware/smackx/workgroup/settings/GenericSettings.java

@@ -66,7 +66,7 @@ public class GenericSettings extends IQ {
 
     @Override
     protected IQChildElementXmlStringBuilder getIQChildElementBuilder(IQChildElementXmlStringBuilder buf) {
-        buf.append(">");
+        buf.append('>');
         if (ModelUtil.hasLength(getQuery())) {
             buf.append("<query>" + getQuery() + "</query>");
         }

smack-legacy/src/main/java/org/jivesoftware/smackx/xevent/packet/MessageEvent.java

@@ -305,30 +305,30 @@ public class MessageEvent implements ExtensionElement {
      */
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" xmlns=\"").append(getNamespace()).append(
+        buf.append('<').append(getElementName()).append(" xmlns=\"").append(getNamespace()).append(
             "\">");
         // Note: Cancellation events don't specify any tag. They just send the packetID
 
         // Add the offline tag if the sender requests to be notified of offline events or if 
         // the target is offline
         if (isOffline())
-            buf.append("<").append(MessageEvent.OFFLINE).append("/>");
+            buf.append('<').append(MessageEvent.OFFLINE).append("/>");
         // Add the delivered tag if the sender requests to be notified when the message is 
         // delivered or if the target notifies that the message has been delivered
         if (isDelivered())
-            buf.append("<").append(MessageEvent.DELIVERED).append("/>");
+            buf.append('<').append(MessageEvent.DELIVERED).append("/>");
         // Add the displayed tag if the sender requests to be notified when the message is 
         // displayed or if the target notifies that the message has been displayed
         if (isDisplayed())
-            buf.append("<").append(MessageEvent.DISPLAYED).append("/>");
+            buf.append('<').append(MessageEvent.DISPLAYED).append("/>");
         // Add the composing tag if the sender requests to be notified when the target is 
         // composing a reply or if the target notifies that he/she is composing a reply
         if (isComposing())
-            buf.append("<").append(MessageEvent.COMPOSING).append("/>");
+            buf.append('<').append(MessageEvent.COMPOSING).append("/>");
         // Add the id tag only if the MessageEvent is a notification message (not a request)
         if (getStanzaId() != null)
             buf.append("<id>").append(getStanzaId()).append("</id>");
-        buf.append("</").append(getElementName()).append(">");
+        buf.append("</").append(getElementName()).append('>');
         return buf.toString();
     }
 

smack-legacy/src/main/java/org/jivesoftware/smackx/xroster/RemoteRosterEntry.java

@@ -100,11 +100,11 @@ public class RemoteRosterEntry {
 
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<item jid=\"").append(user).append("\"");
+        buf.append("<item jid=\"").append(user).append('"');
         if (name != null) {
-            buf.append(" name=\"").append(name).append("\"");
+            buf.append(" name=\"").append(name).append('"');
         }
-        buf.append(">");
+        buf.append('>');
         synchronized (groupNames) {
             for (String groupName : groupNames) {
                 buf.append("<group>").append(groupName).append("</group>");

smack-legacy/src/main/java/org/jivesoftware/smackx/xroster/packet/RosterExchange.java

@@ -165,14 +165,14 @@ public class RosterExchange implements ExtensionElement {
      */
     public String toXML() {
         StringBuilder buf = new StringBuilder();
-        buf.append("<").append(getElementName()).append(" xmlns=\"").append(getNamespace()).append(
+        buf.append('<').append(getElementName()).append(" xmlns=\"").append(getNamespace()).append(
             "\">");
         // Loop through all roster entries and append them to the string buffer
         for (Iterator<RemoteRosterEntry> i = getRosterEntries(); i.hasNext();) {
             RemoteRosterEntry remoteRosterEntry = i.next();
             buf.append(remoteRosterEntry.toXML());
         }
-        buf.append("</").append(getElementName()).append(">");
+        buf.append("</").append(getElementName()).append('>');
         return buf.toString();
     }