Iterator Pattern

Iterator Design Pattern
Advantage of Iterator DP
Usage of Iterator DP
UML of Iterator DP
Example of Iterator DP

According to GoF, Iterator Pattern is used "to access the elements of an aggregate object sequentially without exposing its underlying implementation".

The Iterator pattern is also known as Cursor.

In collection framework, we are now using Iterator that is preferred over Enumeration.

java.util.Iterator interface uses Iterator Design Pattern.

Advantage of Iterator Pattern

It supports variations in the traversal of a collection.
It simplifies the interface to the collection.

Usage of Iterator Pattern:

It is used:

When you want to access a collection of objects without exposing its internal representation.
When there are multiple traversals of objects need to be supported in the collection.

Example of Iterator Pattern

Let's understand the example of iterator pattern pattern by the above UML diagram.

UML for Iterator Pattern:

Implementation of above UML

Step 1

Create a Iterartor interface.

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

Step 2

Create a Container interface.

public interface Container {
	public Iterator getIterator();
}// End of the Iterator interface.

Step 3

Create a CollectionofNames class that will implement Container interface.

File: CollectionofNames.java

public class CollectionofNames implements Container {
public String name[]={"Ashwani Rajput", "Soono Jaiswal","Rishi Kumar","Rahul Mehta","Hemant Mishra"}; 
	
@Override
	public Iterator getIterator() {
		return new CollectionofNamesIterate() ;
	}
	private class CollectionofNamesIterate implements Iterator{
		int i;
		@Override
		public boolean hasNext() {
			if (i<name.length){
				return true;
			}
			return false;
		}
		@Override
		public Object next() {
			if(this.hasNext()){
	            return name[i++];
			}
		    return null;	
		}
	}
}
}

Step 4

Create a IteratorPatternDemo class.

File: IteratorPatternDemo.java

public class IteratorPatternDemo {
	public static void main(String[] args) {
	      CollectionofNames cmpnyRepository = new CollectionofNames();
	      
	      for(Iterator iter = cmpnyRepository.getIterator(); iter.hasNext();){
	          String name = (String)iter.next();
	          System.out.println("Name : " + name);
	       } 	
	}
}

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