concat() and + both add up strings. It looks same, but + do one more step. As seen below, + will create string builder and append the strings inside, and then it will give the string. So, concat() is less expensive.
/* Using + sign */ String myStr = "str"; myStr += "end"; // Same as above String myStr = "str"; myStr = new StringBuilder().append(myStr).append("end").toString();
/* Using concat() */ String myStr = "str"; myStr = myStr.concat("end");