Wrapper Classes





Java Wrapper Classes :

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 need those types. So a primitive wrapper class is a wrapper class that encapsulates, hides or wraps data types from the eight primitive data types.

  • Provides a way of wrapping primitive values in an object so that a primitive can be treated as an object.
  • Provides a set of utility methods for primitives.
  • Wrapper classes are available in java.lang package.
Situation when we required Wrapper Classes:
  • When primitives are required to be added to a collection object.
  • When we want to return a primitive from a method that returns an object.
  • When converting primitives to and from String objects.
  • When converting primitives & String objects to and from different bases like binary, octal & hexadecimal.
Wrapper Classes: prowessapps.in
Object Creation:
Integer i1 = new Integer(5);
Integer i2 = new Integer("5");

Float f1 = new Float(5.6f);
Float f2 = new Float("5.6f");

Double d1 = new Double(6.7);
Double d2 = new Double("6.7");

Character c = new Character('a');

Boolean b1 = new Boolean(true);
Boolean b2 = new Boolean("true");
Boolean b3 = new Boolean("TrUe");
Methods:

 parseInt(s)	
returns a signed numeric value equivalent to string s

 valueOf(primitive)	
returns wrapper object equivalent to primitive

 valueOf(String)	
returns wrapper object equivalent to String

 valueOf(String,int)	
returns wrapper object equivalent to String as per give base(DEC-10,BIN-2,OCT-8,HEX-16) value. 

 toString(i)	
returns a new String object representing the integer i

 byteValue()
returns the value of this type as a byte

 doubleValue()
returns the value of this type as a double

 floatValue()
returns the value of this type as a float

 intValue()
returns the value of this type as an int

 shortValue()
returns the value of this type as a short

 longValue()
returns the value of this type as a long
Example:
class Test
{
 public static void main(String[] a) 
 {
  String s = "A";
  Integer i1 = Integer.valueOf(s,16);
  byte b = i1.byteValue();
  System.out.println(b);
 }
}
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Next topic is generics




 




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