Wrappers

Wrappers

• Wrapper classes are those classes that allow primitive data types to be accessed as objects.

• The wrapper class is one kind of wrapper around a primitive data type. The wrapper classes represent the primitive data types in its instance of the class.

• Following table shows various primitive data types and the corresponding wrapper classes -

• Methods to handle wrapper classes are enlisted in the following table -

• Suppose an object for holding an integer value is created then we can retrieve the integer value from it using typevalue() method. For instance the object obj contains an integer value then we can obtain the integer value from obj. It is as follows -

int num=obj.intValue();

• Similarly we can use floatValue(), doubleValue() and longValue().

• Similarly in order to convert the numerical value to string the toString() method can be used. For instance

str=Integer.toString(int_val)

• The variable int_val can be converted to string str.

• For converting the string to numerical value the parseInt or parseLong methods can be used.

Points to remember about wrapper classes

1. The wrapper classes do not contain the constructors.

2. The methods of the wrapper classes are static.

3. After assigning the values to the wrapper class we cannot change them.

Example: Java Program

import java.io.*;

import java.lang.*;

class WrapperDemo

{

public static void main(String[] args)

{

System.out.println("Creating an object for value 10");

Integer i=new Integer(10);

System.out.println("Obtaining the value back from the object: "+i.intValue());

String str="100";

System.out.println("The string is: "+str);

System.out.println("Obtaining the numeric value from the string: "+ Integer.parseInt(str));

}

}

Output

Creating an object for value 10

Obtaining the value back from the object: 10

The string is: 100

Obtaining the numeric value from the string: 100

Ex. 3.18.1Define wrapper class. Give the following wrapper class methods with

syntax and use :

1) To convert integer number to string.

2) To convert numeric string to integer number.

3) To convert object numbers to primitive numbers sing type value () method.

Sol. Wrapper class - Refer section 3.18.

class WrapperDemo1

{

public static void main(String args[]).

{

System.out.println("\tInteger to String Conversion");

int i=100;

String str=Integer.toString(i);

System.out.println("int Value: "+i);

System.out.println("Equivalent String: "+str);.

System.out.println("\tString to Integer Conversion");

str="500";

int j= Integer.parseInt(str);

System.out.println("String: "+str);

System.out.println("Equivalent int: "+j);

System.out.println("\tobject to Primitive number

using typeValue Conversion");

Integer a new Integer(1000);//creating object for float value int val a.intValue();

System.out.println("Integer: "+a);

System.out.println("Equivalent int value: "+val);

Float b=new Float(2000);//creating object for float value

float f=b.floatValue();

System.out.println("Float: "+b);

System.out.println("Equivalent float value: "+f);

}

}

Output

Integer to String Conversion

int Value: 100

Equivalent String: 100

String to Integer Conversion

String: 500

Equivalent int: 500

object to Primitive number using typeValue Conversion

Integer: 1000

Equivalent int value: 1000

Float: 2000.0

Equivalent float value: 2000.0

Uses of Wrapper Class

1) Wrapper classes are used to convert numeric strings into numeric values.

2) Wrapper classes are used to convert numeric value to string using wrapper class.

3) Wrapper class is a medium to store primitive data type in an object.

4) Using the typeValue() method we can retrieve value of the object as its primitive data type.

Review Questions

1.Explain the use of wrapper classes in Java.

2. Explain the concept of wrapper classes with illustrative example.