Use StringBuilder.append instead of += when building up a String.

src/main/com/mongodb/DBCollection.java

@@ -458,16 +458,16 @@ DBObject defaultOptions( DBObject keys ){
      * @return a string representation of this index's fields
      */
     public static String genIndexName( DBObject keys ){
-        String name = "";
+        StringBuilder name = new StringBuilder();
         for ( String s : keys.keySet() ){
             if ( name.length() > 0 )
-                name += "_";
-            name += s + "_";
+                name.append( '_' );
+            name.append( s ).append( '_' );
             Object val = keys.get( s );
             if ( val instanceof Number || val instanceof String )
-                name += val.toString().replace( ' ' , '_' );
+                name.append( val.toString().replace( ' ', '_' ) );
         }
-        return name;
+        return name.toString();
     }
 
     // --- END INDEX CODE ---

src/main/com/mongodb/Mongo.java

@@ -693,16 +693,15 @@ public void run() {
 
     @Override
     public String toString() {
-        String str = "Mongo: ";
+        StringBuilder str = new StringBuilder("Mongo: ");
         List<ServerAddress> list = getServerAddressList();
         if (list == null || list.isEmpty())
-            str += "null";
+            str.append("null");
         else {
-            for (ServerAddress addr : list) {
-                str += addr.toString() + ",";
-            }
-            str = str.substring(0, str.length() - 1);
+            for ( ServerAddress addr : list )
+                str.append( addr.toString() ).append( ',' );
+            str.deleteCharAt( str.length() - 1 );
         }
-        return str;
+        return str.toString();
     }
 }

src/main/com/mongodb/util/Args.java

@@ -45,33 +45,32 @@ public String getOption( String name ){
     }
 
     public String toString(){
-        String s = "";
-        
+        StringBuilder s = new StringBuilder();
+
         for ( String p : _options.keySet() ){
-            s += "-" + p;
+            s.append( '-' ).append( p );
 
             String v = _options.get( p );
             if ( v.length() == 0 )
                 continue;
 
-            s += "=";
-            
+            s.append( '=' );
+
             if ( v.indexOf( " " ) >= 0 )
-                s += "\"" + v + "\"";
+                s.append( '"' ).append( v ).append( '"' );
             else
-                s += v;
+                s.append( v );
         }
 
         for ( String p : _params ){
-            s += " ";
+            s.append( ' ' );
             if ( p.indexOf( " " ) >= 0 )
-                s += "\"" + p + "\"";
-            else 
-                s += p;
+                s.append( '"' ).append( p ).append( '"' );
+            else
+                s.append( p );
         }
-
-
-        return s;
+
+        return s.toString();
     }
 
     final Map<String,String> _options = new HashMap<String,String>();