wrapper classes

[sireesha]

which is usefull(commonly used) way to represent numbers like
int x,y;
or
Integer x,y;
what is the difference between them ?
i wrote code like

Code:

class test4
{
public static void main(String args[])
 {
  Integer x,y;
  x=23;
  y=30;
  System.out.println(x+ys);
 }
}

i got following errors
1.incompatible types
2. operator + cannot be applied to java.lang.Integer,java.lang.Integer.

what is wrong with my code ?
please tell me..

[dmacvittie]

int is a "low-level" or "base" data type. There is no class associated with it, it is just a space in the computers' memory (in the case of Java in the JVM's memory).
Integer has all of the class information you would expect - you can inherit from Integer, etc.
For me, I only use Integer where I need a class (for storage in lists, etc)... There is a small amount (really, very small) of overhead using Integer, so if I don't have a good reason to, I don't.

Hope that helps.
Don.

[definewebsites]

Quote:

Originally Posted by sireesha

which is usefull(commonly used) way to represent numbers like
int x,y;
or
Integer x,y;
what is the difference between them ?
i wrote code like

Code:

class test4
{
public static void main(String args[])
 {
  Integer x,y;
  x=23;
  y=30;
  System.out.println(x+ys);
 }
}

i got following errors
1.incompatible types
2. operator + cannot be applied to java.lang.Integer,java.lang.Integer.

what is wrong with my code ?
please tell me..

Well, you have declared x and y as type "Integer". Integer is a class and when you make such declarations you are creating objects of that class. As such you cannot use the assignment operator to assign them values of type "int", and also you cannot apply the "+" operator to them. In order to use x and y, you need to call the methods of the class Integer.

I think what you want to do is this:

Code:

class test4
{
public static void main(String args[])
 {
  int x,y;
  x=23;
  y=30;
  System.out.println(x+y);
 }
}

HTH

[staykovmarin]

There is really no reason to use the Integer class for something as simple:

Code:

int x = 7, y = 4;
int d = y+x;

The difference is where the information is stored (primitives are on the stack, while Class instances are put on the heap). Primitives are the ones that you can add subtract and so on. Classes (with the exception of String) do not have those options.

(sorry for beating the topic to death, it took me a long time to reply, so i didnt see the other two answers getting posted)

[sireesha]

Hi,
i can't understand one thing.
what is the use of Integer class objects (like x,y in my code) if they are not useful to assign integers.
please give me an example(some code) to understand the use of wrapper classes.

[staykovmarin]

Code:

		// ArrayList<int> intgers = new ArrayList<int>(); // <- breaks. You cant
		// have prmitives in generics
		ArrayList<Integer> intgers = new ArrayList<Integer>(); // <-works, and it 
                // has the same effect as having integers into it.