Iterator Pattern

Video

https://www.youtube.com/watch?v=uNTNEfwYXhI

Definition

This pattern is used to get a way to access the elements of a collection object in sequential manner without any need to know its underlying representation.

Implementation

Iterator Interface

public interface Iterator {
  public boolean hasNext();
  public Object next();
}

it can be

public interface Iterator {
  public boolean hasNext();
  public void next();
  public Object Current();
}

Container Interface

public interface Container {
  public Iterator getIterator();
}

Concrete class implementing the Container interface

public class NameRepository implements Container {
   public String names[] = {"Robert" , "John" ,"Julie" , "Lora"};

   @Override
   public Iterator getIterator() {
      return new NameIterator();
   }

   private class NameIterator implements Iterator {

      int index;

      @Override
      public boolean hasNext() {
      
         if(index < names.length){
            return true;
         }
         return false;
      }

      @Override
      public Object next() {
      
         if(this.hasNext()){
            return names[index++];
         }
         return null;
      }		
   }
}

Implementation Detail

public class IteratorPatternDemo {
	
   public static void main(String[] args) {
      NameRepository namesRepository = new NameRepository();

      for(Iterator iter = namesRepository.getIterator(); iter.hasNext();){
         String name = (String)iter.next();
         System.out.println("Name : " + name);
      } 	
   }
}