java - Implementation of toString() method in a linkedList -

i trying implement method prints out contents inside linked list.
here explanation of classes use:

1) nonemptylistnode , emptylistnode inherit abstractlistnode.
2) trailing node represented emptylistnode.

i implemented it, however, felt bad since taught instanceof keyword bad. here questions:

1) can implement tostring() without instanceof keyword?
2) implement tostring() in recursive way?

here code:

abstract public class abstractlistnode {             abstract public object item();     abstract public abstractlistnode next();     abstract public boolean isempty();     abstract public int size();     abstract public string tostring();             }  class nonemptylistnode extends abstractlistnode {      private object myitem;     private abstractlistnode mynext;      public nonemptylistnode (object item, abstractlistnode next) {         myitem = item;         if (next == null) {             mynext = new emptylistnode();         } else {             mynext = next;         }     }      public nonemptylistnode (object item) {         (item, new emptylistnode());     }      public object item() { return myitem; }      public abstractlistnode next() { return mynext; }      public boolean isempty() {return false;}      @override     public int size() {         return 1 + mynext.size();     }      @override     public string tostring() {         abstractlistnode iter = this;         string str = "( ";          //here         while(iter instanceof nonemptylistnode){             str += iter.item() + " ";             iter = iter.next();         }         return str + iter.tostring();     } }  class emptylistnode extends abstractlistnode {        public emptylistnode() {}      public object item() {         throw new illegalargumentexception ("there no 'item' value stored in emptylistnode.");     }      public abstractlistnode next() {         throw new illegalargumentexception ("no elements follow emptylistnode.");     }      public boolean isempty() {         return true;     }      @override     public int size() {         return 0;     }      @override     public string tostring() {         return ")";     } } 

you can replace

iter instanceof nonemptylistnode 

with

iter.isnonempty() 

or

!iter.isempty() 

where returns true nonemptylistnode