var str1:String = "Vinoth";
var str2:String = "Babu";
var str3:String = "Chennai";
var str4:String = concat(str1," ",str2,str3)

trace(str4)会导致你
str4 ==“Vinoth babu Chennai”

字符串Concat类

public class StringBuffer
{
    public var buffer:Array = new Array();

    public function add(str:String):void
    {
        for (var i:Number = 0; i < str.length; i++)
        {
            buffer.push(str.charCodeAt(i));
        }
    }

    public function toString():String
    {
        return String.fromCharCode.apply(this,buffer);
    }
}

在这里,你比上面写的更深刻.

http://blogs.adobe.com/pfarland/2007/10/avoiding_string_concatenation.html