an Object array

[Castulo Ruiz]

I have this an array of linked list. the linked list is an ADT.
When make the array and store the linked list well it does not work. the loop stops there is nothing inside.
not sure what is going on.

     List row[]= new List[n]; 
     List temp = new List();
     for(int i = 0; i<n ; i++){
        for(int j= 1; j<=n;  j++){
           temp.insertAfterLast(1);  
        }    
        row[i] = temp;    
        temp.makeEmpty(); 
     }
     // displays what is in linked list
     row[0].displayForward() 
 

[Campbell Ritchie]

You are calling makeEmpty(). Doesn't that remove everything you have just added?

[Rob Spoor]

The assignment row[i] = temp doesn't create a copy of the List object temp is referring to, it only copies the reference. Afterwards, both row[i] and temp refer to the same object. And after the loop, you have n references in the List plus the extra temp reference, all referring to one single List object. So when you clear temp, you're clearing all List objects - the only one there is.

The solution is easy - create a new copy each time:

List row[]= new List[n];    
     for(int i = 0; i<n ; i++){   
        List temp = new List(); // moved inside the loop; each iteration now creates a new List
        for(int j= 1; j><=n;  j++){   
           temp.insertAfterLast(1);     
        }       
        row[i] = temp;       
        // no need to clear it anymore
        //temp.makeEmpty();    
     }   
     // displays what is in linked list   
     row[0].displayForward();