String Concat vs. +

What is the difference between the concat() method in String and the '+' operator for the String?  I thought they were the same, but when I try to "build" a string by concatening (using the concat method) strings to an initially empty string, I appear to get nothing, whereas if I do it via '+' (or in this case '+=') it turns out ok.  
Here is the sample code:

String processedString = "";
String workingString = myTextArea.getText();
int stringLength = workingString.length();

     for (int i = 0; i < stringLength; i++){
        if (workingString.charAt(i) == '\n'){
                processedString += "\r\n";
                // Or processedString.concat("\r\n");
            }
            else{
                processedString += workingString.charAt(i);
                // Or processedString.concat("" + workingString.charAt(i));
            }
        }
    }

Thanks for shedding any light on this!


ap9