The String is one of the most important classes in Java and anyone who starts with Java programming uses String to print something on the console by using famous System.out.println() statements. Many Java beginners not aware that String is immutable and final in Java and every modification in String creates a new String object. For example, when you get the substring, you get a new String, when you convert uppercase String to lowercase, a new String is created. Even when you remove space by calling the trim() method, a new String is returned. So, now the big question is how do you manipulate String in Java without creating String garbage? StringBuilder and StringBuffer are the answer to this question. StringBuffer is old class but StringBuilder is newly added in Java 5 along with major improvements in Enum, Generics, varargs methods and Autoboxing in Java.