Java - Wrapper Class

1) Wrapper classes are classes that allow primitive types to be      
     accessed as objects. 
2) Wrapper class is wrapper around a primitive data type.                           

Some of the sound features maintained by the Wrapper Classes are as under :

• All the methods of the wrapper classes are static.
• The Wrapper class does not contain constructors.
• Once a value is assigned to a wrapper class instance it can not be changed, anymore. 
•                                                                                                       These Wrapper classes can be created in many ways, so i will start slow, simply returning objects with a String.                        
  
   

  Primitive	Wrapper
  boolean	java.lang.Boolean
  byte	java.lang.Byte
  char	java.lang.Character
  double	java.lang.Double
  float	java.lang.Float
  int	java.lang.Integer
  long	java.lang.Long
  short	java.lang.Short
  void	java.lang.Void

  Integer from String:
  Integer i = Integer.valueOf(“125″);
  
  
  Double from String:
  Double d = Double.valueOf(“5.829754097″);
  
  
  Float from String:
  Float f = Float.valueOf(“8.43543″);
  
  
  Boolean from String:
  Boolen b = Boolean.valueOf(“true”);
  //This will represent true
  
  
  Character from String:
  Character c = Character.valueOf(“G”);
  The more common use is given the primitive in a variable. This next section shows how to convert a variable to these wrapper classes and back to a primitive.
  
  
  Integer:
  int i = 5;
  Integer I = Integer.valueOf(i); //Wrapper
  int i2 = I.intValue(); //back to primitive
  
  
  Float:
  float f = 5.5f;
  Float F = Float.valueOf(f); //Wrapper
  float f2 = F.floatValue(); //back to primitive
  
  
  Double:
  double d = 5.55555;
  Double D = Double.valueOf(d); //Wrapper
  double d2 = D.doubleValue(); //back to primitive
  
  Boolean:
  boolean b = true;
  Boolean B = Boolean.valueOf(b); //Wrapper
  boolean b2 = B.booleanValue(); //back to primitive
  *When dealing with strings you may also wish to use the following to get primitives from the Object String:
  
  
   Integer:
  int i = Integer.parseInt(“234″);
  
  
  Double
  double d = Double.parseDouble(“234.6576533254″);
  
  
  Float:
  float f = Float.parseFloat(“234.78″);
  
  
  Long:
  long l = Long.parseLong(“23454654″);
  *Note you may wish to add the ().trim feature to these last ones, in the case of extra white space around your String, which may cause exceptions.
   
  Example of trim:
  String s = ” William “; // displays as ‘ William ‘
  String s2 = (s).trim(); //displays ‘William’