Mumbai University > Information Technology > Sem 3 > Object Oriented Programming Methodology

Marks: 5 M

Year: Dec 2013, Dec 2014, May 2015

• 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.
• Wrapper classes are used to convert primitive data types to object types by using the wrapper class contained in Java.lang package.
• The table below shows the simple data types ad their corresponding wrapper class types.

• There are mainly two applications of wrapper classes.

  1) To convert simple data types into objects, that is, to give object form to a data type; here constructors are used.

  2) To convert strings into data types (known as parsing operations), here methods of type parseXXX() are used.

• For example,

  int k = 100;

  Integer it1 = new Integer(k);

  The int data type k is converted into an object, it1 using Integer class. The it1 object can be used in Java programming wherever k is required an object.

• The following code can be used to unwrap (getting back int from Integer object) the object it1.

  int m = it1.intValue();

  System.out.println(m*m); // prints 10000

• intValue() is a method of Integer class that returns an int data type.

• Conversion of Strings to Primitive data types can be carried out as follows:

  int i= Integer.parseInt(Str); //converts string to primitive integer

  long i= Long.parseLong(Str); //converts string to primitive long