Enumerations, Autoboxing, Static Import, and Annotations - Java: A Beginner's Guide - page 579

Integer(int num )
Integer(String str ) throws NumberFormatException
Double(double num )
Double(String str ) throws NumberFormatException
If str does not contain a valid numeric value, then a NumberFormatException is thrown.
All of the type wrappers override toString( ) . It returns the human-readable form of the
value contained within the wrapper. This allows you to output the value by passing a type
wrapper object to println( ) , for example, without having to convert it into its primitive
type.
The process of encapsulating a value within an object is called boxing . Prior to JDK 5,
all boxing took place manually, with the programmer explicitly constructing an instance of
a wrapper with the desired value. For example, this line manually boxes the value 100 into
an Integer :
In this example, a new Integer object with the value 100 is explicitly created and a refer-
ence to this object is assigned to iOb .
The process of extracting a value from a type wrapper is called unboxing . Again, prior
to JDK 5, all unboxing also took place manually, with the programmer explicitly calling a
method on the wrapper to obtain its value. For example, this manually unboxes the value
in iOb into an int .
Here, intValue( ) returns the value encapsulated within iOb as an int .
The following program demonstrates the preceding concepts: