type wrappers in java

[sn20063757]

what is meant by the term type wrappers .And what is their us in java programming .
For example
import java.util.*;
import javax.swing.JOptionPane;
public class Numyears
{
public static void main(String[]args)
{
GregorianCalendar current=new GregorianCalendar();
int currentYear;
int birthYear;
int numYears;
birthYear=Integer.parseInt(JOptionPane.showInputDi alog
(null,"in what year were you born?",JOptionPane.QUESTION_MESSAGE));
currentYear=current.get(Calendar.YEAR);
numYears=currentYear-birthYear;
JOptionPane.showMessageDialog(null,"you will turn"+numYears+"years old",JOptionPane.INFORMATION_MESSAGE);
system.exit(0);
}
}

[JosAH]

Pardon my blindness but I don't see any wrappers in your code.

kind regards,

Jos

ps. for a good wrapper/decorator example see all the InputStream classes.

[etiainen]

Yeah, you didn't use any wrappers in your example but still...
They can be used to make objects out of your primitives. This is useful if you are using some non generic collections (those without <T>) or if you in any way intend to pass your primitive value to a method expecting an object.

example:

//...
int somePrimitive=1;
java.util.ArrayList aList=new java.util.ArrayList();
 
//the right way:
aList.add(new Integer(somePrimitive));
 
//this would cause an exception:
//aList.add(somePrimitive);
//...
 

ou yeah, AND they can be used as mentioned in previous post to wrap the functionality of a more general type, as in:

DataInputStream dis=new DataInputStream(new FileInputStream("someFile.txt"));