Collections - Linked list

[Justin Fox]

ok, here is my Number class....

    
 
public class Number{
 
private int A;
public String C = "";
 
public Number(int B)
{
 
A = B;
 
}
 
public String toString()
{
String c = Integer.toString(A);
return c;
}
}
 

can this be referenced as a node?...or element of a list?
because I went to the API and looked under list in the java.util,
and it said it had a add()method. but I read on further down
and it says its a boolean method.

well any ways. here is my main class.

    
 
import java.util.*;
public class List{
 
public static void main (String [] args)
{
 
List mylist = new List();
 
Number one = new Number(1);
Number two = new Number(2);
Number three = new Number(3);
Number four = new Number(4);
Number five = new Number(5);
 
}
}

now the List compiles fine, but when i try to do mylist.add(one);
, it doesn't want to compile, says it can't find the method add().

so do i need to make my own class and define an add method?

and also, in my book, it shows this as an example of a node.

    
class Node
{
int info;
Node next;
}
 

So could i create a whole bunch of Node classes?...and add them to a List?

like for example..

class Node1
{
int info;
Node1 next;
}

but what i dont under stand is... what would Node1 point to?
which ever element is added next?

until I add one that is defined?
like so:

    
class Node3
{
int info;
Node3 null;
}

but when i declare it in a main class..
there is not public modifier...

so would i just do

Node3 node3 = new Node3();?

or

Node3 node3;
- and if i did do it like this, would the info be passed on?

Thanks for the help

-Justin-

[Henry Wong]

   import java.util.*;
 
   public class List{                            // Class Name
      public static void main (String [] args){
         List mylist = new List();               // Create instance
 
         Number one = new Number(1);
         Number two = new Number(2);
         Number three = new Number(3);
         Number four = new Number(4);
         Number five = new Number(5);
      }
   }   

When you instantiate a List object, you are not instantiating a collection. Instead, you are instantiating your own class. The reason that the add() method doesn't exist, is because you never created one.

Henry

[M. Bunyard]

   import java.util.*;
 
   public class List{                            
      public static void main (String [] args){
         List mylist = new List(); 
 
         Number one = new Number(1);
         Number two = new Number(2);
         Number three = new Number(3);
         Number four = new Number(4);
         Number five = new Number(5);
      }
   } 

From the imported java.util.* package, it appears that you are trying to instantiate a java.util.List object. A java.util.List object cannot be instantiated due to the fact that it is an interface, but you can do the following if the Collections List is what your after:

    
public class List{
    public static void main (String [] args){
       java.util.List mylist = new ArrayList();
              
       Number one = new Number(1);
       Number two = new Number(2);
       Number three = new Number(3);
       Number four = new Number(4);
       Number five = new Number(5);
       
       mylist.add(one);
       mylist.add(two);
       mylist.add(three);
       mylist.add(four);       
       mylist.add(five);
    }
}

The "java.util" is pre-pended when defining the mylist variable to remove the ambiguity in which List class (or interface) to use (either predefined java.util.List interface or your List class).