A primitive wrapper class in the Java programming language is one of eight classes provided in the java.lang
package to provide object methods for the eight primitive types. All of the primitive wrapper classes in Java are immutable. J2SE 5.0 introduced autoboxing of primitive types into their wrapper object, and automatic unboxing of the wrapper objects into their primitive value—the implicit conversion between the wrapper objects and primitive values.
Wrapper classes are used to represent primitive values when an Object
is required. The wrapper classes are used extensively with Collection
classes in the java.util
package and with the classes in the java.lang.reflect
reflection package.
The primitive wrapper classes and their corresponding primitive types are:
Primitive type | Wrapper class | Constructor Arguments |
---|---|---|
byte |
Byte |
byte or String |
short |
Short |
short or String |
int |
Integer |
int or String |
long |
Long |
long or String |
float |
Float |
float , double or String |
double |
Double |
double or String |
char |
Character |
char |
boolean |
Boolean |
boolean or String |
The Byte
, Short
, Integer
, Long
, Float
, and Double
wrapper classes are all subclasses of the Number
class.
Although it is not a wrapper class, the Void
class is similar in that it provides an object representation of the void
return. The Void
class is an uninstantiable placeholder class used by the java.lang.reflect
API to hold a reference to the Class
object representing the Java keyword void
..
With Java 5.0, additional wrapper classes were introduced in the java.util.concurrent.atomic
package. These classes are mutable and cannot be used as a replacement for the regular wrapper classes. Instead, they provide atomic operations for addition, increment and assignment.
The atomic wrapper classes and their corresponding types are:
Primitive type | Wrapper class |
---|---|
int |
AtomicInteger |
long |
AtomicLong |
boolean |
AtomicBoolean |
V |
AtomicReference<V> |
The AtomicInteger
and AtomicLong
classes are subclasses of the Number
class. The AtomicReference
class accepts the type parameter V
that specifies the type of the object reference. (See "Generics in Java" for a description of type parameters in Java).