Frequently it is necessary to represent a value of primitive
type as if it were an object. The wrapper classes Boolean ,
Character , Integer , Long , Float ,
and Double serve this purpose. An object of type Double , for example, contains a field whose type is double,
representing that value in such a way that a reference to it can be
stored in a variable of reference type. These classes also provide
a number of methods for converting among primitive values, as well
as supporting such standard methods as equals and hashCode. The
Void class is a non-instantiable class that holds a
reference to a Class object representing the type void.
The class Math provides commonly used mathematical
functions such as sine, cosine, and square root. The classes String , StringBuffer , and StringBuilder similarly
provide commonly used operations on character strings.
Classes ClassLoader , Process , ProcessBuilder , Runtime , SecurityManager , and
System provide "system operations" that manage the dynamic
loading of classes, creation of external processes, host
environment inquiries such as the time of day, and enforcement of
Class Throwable encompasses objects that may be thrown
by the throw statement. Subclasses of Throwable
represent errors and exceptions.
System calss also provides the format() method that is better than println() method..so use it.