JP - Wrapper Classes ~ foundjava

Wrapper classes in java

For each and every fundamental data type there exist a pre-defined class, Such predefined class is known as wrapper class. The purpose of wrapper class is to convert numeric string data into numerical or fundamental data.

Why use wrapper classes ?

We know that in java whenever we get input form user, it is in the form of string value so here we need to convert these string values in different different datatype (numerical or fundamental data), for this conversion we use wrapper classes.

Example of wrapper class

class WraperDemo
{
public static void main(String[] args)
{
String  s[] = {"10", "20"};
System.out.println("Sum before:"+ s[0] + s[1]); // 1020
int x=Integer.parseInt(s[0]); // convert String to Integer
int y=Integer.parseInt(s[1]); // convert String to Integer
int z=x+y;
System.out.println("sum after: "+z); // 30
}
}

Output

Sum before: 1020
Sum after: 30

Explanation: In the above example 10 and 20 are store in String array and next we convert these values in Integer using "int x=Integer.parseInt(s[0]);" and "int y=Integer.parseInt(s[1]);" statement
In "System.out.println("Sum before:"+ s[0] + s[1]);" Statement normally add two string and output is 1020 because these are String numeric type not number.

Converting String data into fundamental or numerical

We know that every command line argument of java program is available in the main() method in the form of array of object of string class on String data, one can not perform numerical operation. To perform numerical operation it is highly desirable to convert numeric String into fundamental numeric value.

Example

"10"  --> numeric String --> only numeric string convert into numeric type or value.
"10x" --> alpha-numeric type --> this is not conversion.
"ABC" --> non-numeric String no conversion.
"A"   --> char String no conversion.

Only 'A' is convert into ASCII value that is 65 but 'A' is not convert into numeric value because it is a String value.

Fundamental data type and corresponding wrapper classes

The following table gives fundamental data type corresponding wrapper class name and conversion method from numerical String into numerical values or fundamental value.

Fundamental DataType	Wrapper CalssName	Conversion method from numeric string into fundamental or numeric value
byte	Byte	public static byte parseByte(String)
short	Short	public static short parseShort(String)
int	Integer	public static integer parseInt(String)
long	Long	public static long parseLong(String)
float	Float	public static float parseFloat(String)
double	Double	public static double parseDouble(String)
char	Character
boolean	Boolean	public static boolean parseBoolean(String)

How to use wrapper class methods

All the wrapper class methods are static in nature so we need to call these method using class.methodName().

• for Integer: int x=Integer.parseInt(String);
• for float: float x=Float.parseFloat(String);
• for double: double x=Double.parseDouble(String);

Each and every wrapper class contains the following generalized method for converting numeric String into fundamental values.

Here xxx represents any fundamental data type.