7.4 Wrapper Class
As the name says, a wrapper class wraps (encloses) around a data type and gives it an object appearance.
Wherever, the data type is required as an object, this object can be used. Wrapper classes include methods to unwrap the object and give back the data type.
It can be compared with a chocolate. The manufacturer wraps the chocolate with some foil or paper to prevent from pollution. The user takes the chocolate, removes and throws the wrapper and eats it.
The list of eight wrapper classes are given below:
Primitive Type => Wrapper class
boolean => Boolean
char => Character
byte => Byte
short => Short
int => Integer
long => Long
float => Float
double => Double
Creating objects of the Wrapper classes
All the wrapper classes have constructors which can be used to create the corresponding Wrapper class
For example
Integer intObject = new Integer (15);
Retrieving the value wrapped by a wrapper class object
Each of the eight wrapper classes have a method to retrieve the value that was wrapped in the object.
For example, to retrieve the value stored in the Integer object intObject, we use the following statement.
int x = intObject.intValue();
Similarly, we have methods for the other seven wrapper classes: byteValue(), shortValue(), longValue(), floatValue(), doubleValue(), charValue(), booleanValue().
Auto boxing and auto unboxing
Above given method can become quite cumbersome.
As an alternative, there exists auto boxing and autounboxing.
Auto boxing refers to an implicit call to the constructor and auto unboxing refers to an implicit call to the *value() method.
Therefore, a new wrapper object can be created by specifying the value to be wrapped just as we would do for a primitive data type variable. Also, the value can be retrieved and used in a simple way by specifying the object name.
Look at the following code:
Integer intObject = 34;
int x=intObject;
int x = intObject + 7;
The above statements are equivalent to the following set of statements
Integer intObject = new Integer (34);
int x = intObject.intValue();
int x = intObject .intValue()+ 7;
Similarly, auto boxing and auto boxing apply to other wrapper classes also.
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