Java : Wrapper

Wrapper

http://way2java.com/java-lang/wrapper-classes/

Use : 

1. To convert simple data types into objects
2.  To convert strings into data types

Example :
int k = 100;
Integer obj = new Integer(k); 
 int m = obj.intValue(); //UnWrapp

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

Primitive datatype and     Wrapper and class

• byte     and     Byte
• short     and     Short
• int     and     Integer
• long     and     Long
• float     and     Float
• double     and     Double
• char     and     Character
• boolean and     Boolean

Code :

public class WrappingUnwrapping
{
  public static void main(String args[])
  {                                  //  data types
    byte grade = 2;
    int marks = 50;
    float price = 8.6f;                         // observe a suffix of <strong>f</strong> for float
    double rate = 50.5;
                                           // data types to objects      
    Byte g1 = new Byte(grade);                    // wrapping 
    Integer m1 = new Integer(marks);
    Float f1 = new Float(price);
    Double r1 = new Double(rate);
                                                                    // let us print the values from objects  
    System.out.println("Values of Wrapper objects (printing as objects)");
    System.out.println("Byte object g1:  " + g1);
    System.out.println("Integer object m1:  " + m1);
    System.out.println("Float object f1:  " + f1);
    System.out.println("Double object r1:  " + r1);
            // objects to data types (retrieving data types from objects)
    byte bv = g1.byteValue();                 // unwrapping
    int iv = m1.intValue();
    float fv = f1.floatValue();
    double dv = r1.doubleValue();
                                                                    // let us print the values from data types  
    System.out.println("Unwrapped values (printing as data types)");
    System.out.println("byte value, bv: " + bv);
    System.out.println("int value, iv: " + iv);
    System.out.println("float value, fv: " + fv);
    System.out.println("double value, dv: " + dv);
  }
}