This section begins with a discussion of the Number class (in the java.lang package) and its subclasses. In particular, this section talks about the situations where you would use instantiations of these classes rather than the primitive data types. Additionally, this section talks about other classes you might need to work with numbers, such as formatting or using mathematical functions to complement the operators built into the language. Finally, there is a discussion on autoboxing and unboxing, a compiler feature that simplifies your code.
Strings, which are widely used in Java programming, are a sequence of characters. In the Java programming language, strings are objects. This section describes using the String class to create and manipulate strings. It also compares the String and StringBuilder classes.