Iterator Pattern

Iterator pattern is very commonly used design pattern in Java and .Net programming environment. 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.

Iterator pattern falls under behavioral pattern category.

Implementation

We’re going to create a Iterator interface which narrates navigation method and a Container interface which retruns the iterator . Concrete classes implementing the Container interface will be responsible to implement Iterator interface and use it

IteratorPatternDemo, our demo class will use NamesRepository, a concrete class implementation to print a Names stored as a collection in NamesRepository.

Step 1

Create interfaces.

Iterator.java

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

Container.java

public interface Container {
   public Iterator getIterator();
}

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Step 2

Create concrete class implementing the Container interface. This class has inner class NameIterator implementing the Iterator interface.

NameRepository.java

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;
  }		
   }
}

Step 3

Use the NameRepository to get iterator and print names.

IteratorPatternDemo.java

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);
  } 	
   }
}

Step 4

Verify the output.

Name : Robert
Name : John
Name : Julie
Name : Lora