Java does not have a built-in string type. Instead, the standard Java library contains a predefined class called String. Any quoted sequence of characters is an instance of the String class, including "", which is the empty string. Java allows you to use + and += to concatenate strings. When concatenating a string with a value that is not a string, like "No." + 1, the non-string is converted to a string. If the non-string is a class object, then the object's toString() method is automatically called. Many methods exists for manipulating String objects, including substring, charAt, and others.