Primitive wrapper class in Java

In object-oriented programming, a wrapper class is a class that encapsulates types, so that those types can be used to create object instances and methods in another class that needs those types. So a primitive wrapper class is a wrapper class that encapsulates, hides or wraps data types from the eight primitive data types,^[1] so that these can be used to create instantiated objects with methods in another class or in other classes.^[2][3] The primitive wrapper classes are found in the Java API.

Primitive wrapper classes are used to create an Object that needs to represent primitive types in Collection classes (i.e., in the Java API), in the java.util package and in the java.lang.reflect reflection package. Collection classes are Java API-defined classes that can store objects in a manner similar to how data structures like arrays store primitive data types like int, double, long or char, etc.,^[2] but arrays store primitive data types while collections actually store objects.

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 difference between wrapper classes and primitive types

Primitive wrapper classes are not the same thing as primitive types. Whereas variables, for example, can be declared in Java as data types double, short, int, etc., the primitive wrapper classes create instantiated objects and methods that inherit but hide the primitive data types, not like variables that are assigned the data type values.^[2]

Therefore, the term Primitive wrapper class does not mean that wrapper classes are primitive types. It should be understood to be a class that wraps primitive types. Wrapper classes can be used to store the same value as of a primitive type variable but the instances/objects of wrapper classes themselves are Non-Primitive. We cannot say that Wrapper classes themselves are Primitive types. They just wrap the primitive types.

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 but are immutable.^{[4] [5]}

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). V

See also

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

References

1. S. J. Chapman, Introduction to Java, Prentice Hall, 1999.
2. J. Murach, Murach's Java Programming, 4th Edition, Mike Murach and Associates, Inc., 2011.
3. J. R. Hubbard, Programming with Java, Schaum's Outline Series/McGraw Hill, 1998.
4. David O'Meara (April 2003). "Mutable and Immutable Objects: Which classes are Immutable?". Java Ranch. Retrieved 2012-05-14. The classes java.math.BigInteger and BigDecimal are not immutable either, although maybe they should have been.
5. Oracle. "Java documentation from oracle". Immutable arbitrary-precision integers.