Iterator vs Collection in Java

Iterator and Collection, both has helped and comforted the programmers at many a times. But their usage and application has a very wide difference. 

1. Iterator 

• Declaration 

public interface Iterator

Type Parameters:
E - the type of elements returned by this iterator

• Iterators are used in Collection framework in Java to retrieve elements one by one. 
• Method Summary 

2. Collection 

• Declaration: 

public interface Collection<E> extends Iterable<E>

Type Parameters:
E - the type of elements returned by this iterator

• A Collection is a group of individual objects represented as a single unit. Java provides Collection Framework which defines several classes and interfaces to represent a group of objects as a single unit. 
• Method Summary 

Iterator Vs. Collection  

• Iterator can only move to next() element or remove() an element. 
  However Collection can add(), iterate, remove() or clear() the elements of the collection. 
• Iterator provides a better speed than Collections, as the Iterator interface has limited number of operations. 
• java.sql.SQLException extends Iterable. Hence it allows the caller to safely iterate over causes of SQLException. 
  Using a collection, in this case, would be expensive because, in a chain of n exceptions, use of a collection in the SQLException interface would potentially require the construction of O(n^2) elements. 
  However, use of Iterable provides O(n) access to the exception chain.