Adding a List using hasnext(),next() (user defined)

[aslika bahini]

   
 import java.util.*;
 
interface SIterator
{
public boolean hasNext();
public Object next();  
}
 
interface SCollection
{
public void add(String s);
 public void remove(String r);
public SIterator iterator(); 
}
 
class SListIterator implements SIterator 
{
String[] data;
int index;
SListIterator(String[] d)
{
data = d;
index=0;
System.out.println("data[index]= " +data[index]);
}
public boolean hasNext()
{
index= data.length;
for(int i=0;i<data.length;i++)
{
  if(data[i]!=null)
  {
  return true;
  }
    }
return false;
}
public Object next()
{
Object collobj = null;

try
{
collobj = data[index];
 System.out.println("collobj: "+collobj);
 
}
catch(ArrayIndexOutOfBoundsException e)
{
System.out.println("array index exception");
}

return collobj;
 

    }
}
 

public class SList implements SCollection
{
 
    
    String []data = new String[20];
    int i;
    
    public SIterator iterator()
    {
      return new SListIterator(data);   
    }
   
    
public void add(String s)
{

for(int i=0; i<data.length;i++)
{
if(data[i] == null)
{
data[i] = s; 
return;

}
 
}
System.out.println("List is full");


}
public void remove(String r)
{

    
for(i=0; i<data.length;i++)
{
if(r.equals(data[i]))
{
data[i] = null; 


}

}

}
public void print()
{
for(i=0;i<data.length;i++)
{
if(data[i]!=null)
{
System.out.println("Elements in the array : "+data[i]);
}

}
}
 public static void main(String[] args)
{
    //Create and Fill up list
SList list = new SList();

list.add("element1");
list.add("element2");
list.add("element3");
list.print();


//Get an iterator for the list and iterate.

SIterator sli = list.iterator(); //SIterator    reference variable sli is list object
while (sli.hasNext())
{
Object obj =sli.next();
System.out.println("return object= "+obj);
}

}
    

}
 

output: error
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null
array index exception
return object= null

may i know where i went wrong?

Thanks
samura

[Christophe Verré]

in hasNext :

for(int i=0;i<data.length;i++)
{
  if(data[i]!=null)
  {
return true;

This is always going to be true, isn't it ?

In next(), you never increase the current index.


I'm not sending the code, but just giving you some hints :
1. in hasNext, use the index to check whether it has reached the size of the array, or to check whether the current item is null
2. in next, increase the index