In addition to String, Java has the java.lang.StringBuffer and java.lang.StringBuilder classes. These can also be used to concatenate Strings. The advantage of these classes is that both these classes are mutable, so using them does not result in the creation of new String objects. So StringBuffer and StringBuilder have a better performance as compared to the + operator and concat method.
The StringBuilder class is very similar to StringBuffer. It also has a method called append which can be used to concatenate Strings. The only difference is that StringBuffer is synchronised while StringBuilder is not. So StringBuilder has a slight performance advantage over StringBuffer.
The following code demonstrates the StringBuilder.append method.
So, this code is exactly the same as the StringBuffer code and it prints the following output:
Hello World