Java Reference
In-Depth Information
The method intValue() recovers the corresponding int value from an object of
type Integer . This process of going from an object of a wrapper class to the corre-
sponding value of a primitive type is sometimes called unboxing , and as you will see
in the next subsection, you can let Java automatically do all the work of unboxing
for you.
The wrapper classes for the primitive types byte , short , long , float , double ,
and char are Byte , Short , Long , Float , Double , and Character , respectively. The
methods for converting from the wrapper class object to the corresponding primi-
tive type are intValue for the class Integer , as we have already seen, byteValue for
the class Byte , shortValue for the class Short , longValue for the class Long ,
floatValue for the class Float , doubleValue for the class Double , and charValue for
the class Character .
unboxing
other
wrapper
classes
Wrapper Classes
Every primitive type has a corresponding wrapper class. A wrapper class allows you to have
a class object that corresponds to a value of a primitive type. Wrapper classes also contain a
number of useful predefined constants and static methods.
Automatic Boxing and Unboxing
Converting from a value of a primitive type, such as int , to a corresponding object of
its associated wrapper class, such as Integer , is called boxing. You can think of the
object as a “box” that contains the value of the primitive type. In fact, the wrapper
object does contain the value of the primitive type as the value of a private instance
variable. The following are examples of boxing:
Integer numberOfSamuri = new Integer(47);
Double price = new Double(499.99);
Character grade = new Character('A');
Starting with version 5.0, Java will automatically do this boxing and so the previous
three assignments can be written in the following equivalent, but simpler, forms:
automatic
boxing
Integer numberOfSamuri = 47;
Double price = 499.99;
Character grade = 'A';
This is an automatic type cast. What is actually done by Java is what we showed in the
forms using the new , but it is handy to be able to write the assignments in the simpler
form.
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