Wrapper Classes

 

When we give the gifts, we wrap them nicely in the box. The glossy paper around a box makes in attractive. we have worked with simple data types. Now java wants to wrap them and make them more attractive (useful). For this java uses interesting concept of wrapper class.

Vector cannot handle primitive (basic) data types like int, float, long, char and double. Vector can accept the data in the form of objects. Therefore there is need to convert basic data types into equivalent objects. So this conversion is done by using the wrapper classes which are present in java.lang package.

As all these numbers are stored as objects, they take all the advantage of Object oriented technology.

They can be passed to methods as parameters.

METHODS UNDER WRAPPER CLASSES

1) Converting basic data type to Numeric Object using Constructor Method

       int i = 10;

       float f = 8.9f;

       double d = 897678.9878;

       long l = 989456767; 

Integer intobj = new Integer(i); // convert integer to Integer Object

Double doubleobj= new Double(d); // convert double to Double Object

Float floatobj= new Float(f); // convert float to Float Object

Long longobj= new Long(1); //converts long to Long object

2) Converting Numeric Object to basic data type using typeValue() method.

int i = intobj. intValue();  // converts Integer object to basic integer 

float f = floatobj. floatValue();  // converts Float object to basic float

long 1 = longobj. longValue();  // converts Long object to basic long

double d = doubleobj. doubleValue(); // converts Double object to basic double

3) Converting basic data type to the string using static method toString().

String strl = Integer.toString(i);   // primitive integer to string

String str2 = Float.toString(f);    // primitive float to string

String str3 = Double.toString(d);    // primitive double to string

String str4 = Long.toString(1);    // primitive long to string

4) Converting String Objects to Numeric Objects using the static method ValueOf()

String s1 = "100";

String s2 = "10.54";

String s3 = " 12345";

String s4 = "312223.44222";

Integer objl = Integer. ValueOf(s1);    // converts string to Integer Object 

Float obj2 = Float.valueOf(s2);    // converts String to Float Object 

Long obj3 = Long.valueOf(s3);    // converts String to Long Object 

Double obj4= Double.valueof(s4);  // converts String to Double Object.

5) Conversion of Numeric Strings to basic data type using passing methods

int i = Integer.parseInt(strl);

float f = Float.parseFloat(str2);

double d = Double.parseDouble(str3);

long 1 = Long.parseLong(str4);

Example:

class WrapperDemo {

          public static void main(String[] args) {

           int i = 10;

           float f = 10.85f;

           double d = 0.25632;

           long ph = 98756;

           Integer IntVal = new Integer(i);

           Float FloatVal = new Float(f);

           Double DoubleVal = new Double(d);

           Long LongVal = new Long(ph);

           System.out.println(IntVal); 

           System.out.println(FloatVal);

           System.out.println(Double Val); 

           System.out.println(LongVal);

}

}