Primitive wrapper class in Java

A primitive wrapper class in the Java and ActionScript programming languages 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.

The wrapper classes BigDecimal and BigInteger are not one of the primitive wrapper classes and are mutable.

Void

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."(Javadoc for Void)

Atomic wrapper classes

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).

See alsoooo

• java.lang
• java.lang.reflect
• Java programming language
• Java syntax