Gain insights into Java Collections Framework. Delve into lists, sets, and hashmaps. Learn about data modification, sorting, thread-safety, and internal workings for efficient usage.

Collection is one of the most important topics for Java programming. Without the proper knowledge of every collection type in Java, it becomes difficult for you to decide which option to pick in a particular scenario.

This course will give you a great understanding of all collection types available in the Collections Framework like lists, linked lists, sets, and hashmaps. 

After completing this course, you will know how data can be modified within a collection, how to sort a collection, and how it can be made thread-safe. You will also cover the internal working of each Java collection so you can work with them more efficiently.

Collections in Java

## `ListIterator`

The `Iterator` provides very limited capabilities as we can iterate only in the forward direction and we can't update or insert an element to the list while iterating. To overcome these problems, we can use `ListIterator`. The `listIterator()` method returns an object of type ListIterator which can then be used to iterate the **ArrayList**.

Below are the methods that are available in the ListIterator interface.

1. `hasNext()` — This method is used to check if there is a next element in the list when the list is iterated in the forward direction.

2. `next()` — This method returns the next element in the list and advances the cursor position.

3. `hasPrevious()` — This method is used to check if there is a next element in the list when the list is iterated in the backward direction.

4. `previous()` — This method returns the previous element in the list and moves the cursor position backward.

5. `nextIndex()` — This method returns the index of the element that would be returned by a subsequent call to `next()`. It returns the list size if the list iterator is at the end of the list.

6. `previousIndex()` — This method returns the index of the element that would be returned by a subsequent call to `previous()`. It returns -1 if the list iterator is at the beginning of the list.

7. `remove()` — This method removes the last element that was returned by `next()` or `previous()` from the list. This call can only be made once per call to `next()` or `previous()`. It can be made only if `add()` has not been called after the last call to `next()` or `previous()`.

8. `set(E e)` — This method replaces the last element returned by `next()` or `previous()` with the specified element. This call can be made only if neither `remove()` nor `add()` have been called after the last call to `next()` or `previous()`.

9. `add(E e)` — This method inserts the specified element into the list. The element is inserted immediately before the element that would be returned by `next()`, if any, and after the element that would be returned by `previous()`, if any.

The below example shows `ListIterator` working.

# `ListIterator`

The `Iterator` provides very limited capabilities as we can iterate only in the forward direction and we can't update or insert an element to the list while iterating. To overcome these problems, we can use `ListIterator`. The `listIterator()` method returns an object of type ListIterator which can then be used to iterate the **ArrayList**.

Below are the methods that are available in the ListIterator interface.

1. `hasNext()` — This method is used to check if there is a next element in the list when the list is iterated in the forward direction.

2. `next()` — This method returns the next element in the list and advances the cursor position.

3. `hasPrevious()` — This method is used to check if there is a next element in the list when the list is iterated in the backward direction.

4. `previous()` — This method returns the previous element in the list and moves the cursor position backward.

5. `nextIndex()` — This method returns the index of the element that would be returned by a subsequent call to `next()`. It returns the list size if the list iterator is at the end of the list.

6. `previousIndex()` — This method returns the index of the element that would be returned by a subsequent call to `previous()`. It returns -1 if the list iterator is at the beginning of the list.

7. `remove()` — This method removes the last element that was returned by `next()` or `previous()` from the list. This call can only be made once per call to `next()` or `previous()`. It can be made only if `add()` has not been called after the last call to `next()` or `previous()`.

8. `set(E e)` — This method replaces the last element returned by `next()` or `previous()` with the specified element. This call can be made only if neither `remove()` nor `add()` have been called after the last call to `next()` or `previous()`.

9. `add(E e)` — This method inserts the specified element into the list. The element is inserted immediately before the element that would be returned by `next()`, if any, and after the element that would be returned by `previous()`, if any.

The below example shows `ListIterator` working.

Let's discuss how to iterate an ArrayList using a ListIterator.

Let's Begin

Lists in Java

LinkedList in Java

CopyOnWriteArrayList in Java

Sets in Java

TreeSet in Java

HashMap In Java

TreeMap in Java

LinkedHashMap in Java

Additional Map Implementations

Arrays Class

Collections Class

ArrayList: Iteration using ListIterator

`ListIterator`