**Iterators** allow the user to access elements in a collection one by one. They are very beneficial when the data being processed is large and cannot be accessed all at once. 

We usually use the keyword `it` to refer to an iterator. 

# Methods
Common methods associated with iterators are `next` and `hasNext`. `it.hasNext` checks if there is an element after the current one in the collection. `it.next` returns the next element.  

# Declaration
There are two ways to declare an iterator:
1. Direct: While declaring the collection, put it in parentheses with the `iterator` keyword.
```
val it = Iterator(1, 2, 3, 4, 5)
``` 
2. Indirect: The collection is declared first, and then connected with the iterator.
```
val v = List(1, 2, 3, 4, 5)
val it = v.iterator
```

# Usage with loops
We commonly use iterators with loops to step through the collection. The most common loop with iterators is the `while` loop, which runs until there is a next element (condition checks for `it.hasNext`).


# Code 
The following code shows the implementation of iterators in Scala:

object Main extends App{
  // direct declaration of iterator
  val it_1 = Iterator(1, 2, 3, 4, 5)

  //iterating through the collection
  while(it_1.hasNext)
  {
      println (it_1.next)
  }

  //indirect declaration of iterator
  val v = List(6, 7, 8, 9, 10)
  val it_2 = v.iterator

  //iterating through the collection
  while(it_2.hasNext)
  {
      println (it_2.next)
  }

  // using for loop with iterator 
  val it_3 = Iterator(11, 12, 13, 14, 15)
  for(k <- it_3) println(k)
  
}

How to use iterators in Scala

Iterators in Scala enable element-by-element access in collections, using `hasNext` and `next` methods, often within loops. They're declared directly or indirectly.