Programmer's Guide to Java™ Certification, A: A Comprehensive Primer, Second Edition

10.3. The Wrapper Classes

Wrapper classes were introduced with the discussion of the primitive data types (see Section 2.2, p. 28). Primitive values in Java are not objects. In order to manipulate these values as objects, the java.lang package provides a wrapper class for each of the primitive data types. All wrapper classes are final. The objects of all wrapper classes that can be instantiated are immutable, that is, their state cannot be changed.

Although the Void class is considered a wrapper class, it does not wrap any primitive value and is not instantiable (i.e., has no public constructors). It just denotes the Class object representing the keyword void. The Void class will not be discussed further in this section.

In addition to the methods ...