java - Implementing an iterator for a stack -

i defined interface stringstack

public interface stringstack{     //add value stack     public void push(string value);     //fetch top-most element of stack. element removed     public string pop();     //fetch top-most element of stack. element not removed     public string peek(); } 

further defined class simplestack uses arraylist manage stack

public class simplestack implements stringstack{     private arraylist<string> list = new arraylist<string>();      public void push(string value){         list.add(value);     }      public string pop(){         if(!list.isempty()){                 return list.remove(list.size() - 1);         }else{                 return null;         }     }     public string peek(){         if(!list.isempty()){                 return list.get(list.size() - 1);         }else{                 return null;         } } 

now want define iterator stack class don't want use built-in arraylist iterator. came implementing inner class , extending simplestack iterable interface.

so have now:

 public class simplestack implements stringstack, iterable<string>   ...   public iterator<string> iterator(){     return new stackenum();  }   class stackenum implements iterator<string>{      int pos = list.size();      public boolean hasnext(){         return pos != 0;     }      public string next(){         if(pos != 0){             string str = list.get(pos);             pos--;         }else{             throw new nosuchelementexception();         }     }      public void remove(){         throw new unsupportedoperationexception();     }  } 

i absolutely not sure how perform iteration inside iterator. since stack represented array list used list.size() top-element.

am right implementation of iterator, next method?

i don't know if iterator stack idea, typical behavior of stack not conform iterator-protocol, you'd have pop element reveal next one. suggest add public method getlist() returns list-representation of stack. list implement iterator interface. return copy of arraylist that:

public list<string> returnlist() {   return new arraylist<string>(list); // return copy of arraylist }