Java LinkedList:

Java LinkedList:

• Similar to arrays in Java, LinkedList is a linear data structure.
• In a linked list, the elements are not stored at contiguous memory locations. 
  
• Each element in the LinkedList is called the Node. 
  
• Each node of the LinkedList contains two items: 

1. Content of the element
2. Pointer/Address/Reference to the Next Node in the LinkedList.

Types of Linked List:

• Simple linked list − Item navigation is forward only.
  
• Doubly linked list − Items can be navigated forward and backward.
  
• Circular single linked list − Last item contains a link of the first element as next and the first element has a link to the last element as previous.
  
  
  
• Circular doubly linked list − Items can be navigated forward and backward in circle.
  

Syntax:
java.lang.Object
     java.util.AbstractCollection
         java.util.AbstractList
            java.util.AbstractSequentialList
                java.util.LinkedList

• Note: E - the type of elements held in this collection

Why do we need a Linked List?

• Java LinkedList class uses a doubly linked list to store the elements. 
• It provides a linked-list data structure. 
• It inherits the AbstractList class and implements List and Deque interfaces.
• Linked list allows dynamic memory allocation.
• Linked list elements don’t need contiguous memory locations.

Hierarchy of LinkedList class in Java:

How to create a linked list in Java?

• Syntax: 

                      LinkedList object-name= new LinkedList();

• Example:

                      LinkedList list = new LinkedList();

• Constructors:
• LinkedList() : This constructs constructs an empty list.
• LinkedList(Collection c): This constructs a list containing the elements of the specified collection, in the order, they are returned by the collection's iterator.

Methods:

• How to add item in the linked list at the end?
• boolean add(E e): This method appends the specified element to the end of this list.
• Syntax: public boolean add(E e)
• Parameters: e − element to be appended
• Return Value: This method returns true.
• Example:

list.add("Hello");
list.add(2);
list.add("Chocolate");
list.add("10");

• How to print the linked list?
• Example: System.out.println("LinkedList:" + list);

• How to insert an item at a specific position?
• void add(int index, E element): This method inserts the specified element at the specified position in this list.
• Syntax: public void add(int index,E element)
• Parameters : 
• element − index at which the specified element is to be inserted
• index − element to be appended
• Return Value: This method does not return a value.
• Exception: IndexOutOfBoundsException − if the index is out of range
• Example: list.add(2,"Element");

• How to insert a collection into a linked list?
• boolean addAll(Collection c): This method appends all of the elements in the specified collection to the end of this list, in the order that they are returned by the specified collection's iterator.
• Syntax: public boolean addAll(Collection c)
• Parameters: c − collection containing elements to be added to this list
• Return Value: This method returns true if this list changed as a result of the call
• Exception: NullPointerException − if the specified collection is null
• Example:

Step 01: create a new collection and add some elements
Collection collection = new ArrayList();
collection.add("One");
collection.add("Two");
collection.add("Three");
Step 02: append the collection in the LinkedList
list.addAll(collection);

• How to add new item at first position?
• void addFirst(E e): This method returns inserts the specified element at the beginning of this list.
• Syntax: public void addFirst(E e)
• Parameters: e − the element to add
• Return Value: This method does not return any value.
• Example:

list.addFirst("Add Element");

• How to add new items at last position?
• void addLast(E e) : This method returns appends the specified element to the end of this list.
• Syntax: public void addLast(E e)
• Parameters: e − the element to add
• Return Value: This method does not return any value.
• Example:

list.addLast("Element");

• How to clear all items from the linked list?
• void clear(): This method removes all of the elements from this list.
• Return Value: This method does not return any value.
• Example: 

list.clear();

• How to check items in a linked list?
• boolean contains(Object o) : This method returns true if this list contains the specified element.
• Syntax: public boolean contains(Object o)
• Parameters: o − element whose presence in this list is to be tested
• Return Value: This method returns true if this list contains the specified element
• Example: System.out.println("List contains 'Sarthak':" + list.contains("Sarthak"));

• How to get head item from the linked list?
• E element(): This method retrieves, but does not remove, the head (first element) of this list.
• Return Value : This method returns the head of this list
• Exception : NoSuchElementException − if this list is empty
• Example: System.out.println("Head of list:" + list.element());

• How to get a specific position item from the linked list?
• E get(int index): This method returns the element at the specified position in this list.
• Syntax: public E get(int index)
• Parameters: index − index of the element to return
• Return Value: This method returns the element at the specified position in this list.
• Exception : IndexOutOfBoundsException − if the index is out of range
• Example: System.out.println("Element at index 3 :" + list.get(3));

• How to get first position item from the linked list?
• E getFirst(): This method returns the first element in this list.
• Syntax: public E getFirst()
• Return Value : This method returns the first element in this list
• Exception : NoSuchElementException − if this list is empty
• Example : System.out.println("First Element :" + list.getFirst());

• How to get the last position item from the linked list?
• E getLast(): This method returns the last element in this list.
• Syntax: public E getLast()
• Return Value : This method returns the last element in this list
• Exception : NoSuchElementException − if this list is empty
• Example :System.out.println("Last Element :" + getLast());

• How to remove head item from the linked list?
• E remove(): This method retrieves and removes the head (first element) of this list.
• Syntax: public E remove()
• Return Value: This method returns the head of this list
• Example: list.remove();

• How to remove specific position item from the linked list?
• E remove(int index): This method removes the element at the specified position in this list.
• Syntax: public E remove(int index)
• Parameters : index − the index of the element to be removed
• Return Value: This method returns the element previously at the specified position
• Exception: IndexOutOfBoundsException − if the index is out of range
• Example: System.out.println("Element to be removed:" + list.remove(2));

• How to remove the first position item from the linked list?
• E removeFirst(): This method removes and returns the first element from this list.
• Syntax: public E removeFirst()
• Return Value : This method returns the first element from this list
• Exception : NoSuchElementException − if this list is empty
• Example :System.out.println("First element:" + list.removeFirst());

• How to remove the last position item from the linked list?
• E removeLast(): This method removes and returns the last element from this list.
• Syntax: public E removeLast()
• Return Value : This method returns the last element from this list
• Exception : NoSuchElementException − if this list is empty
• Example :System.out.println("Last element:" + list.removeLast());

• How to get the size of the linked list?
• int size(): This method returns the number of elements in this list.
• Syntax: public int size()
• Return Value : This method returns the number of elements in this list
• Example: System.out.println("List size:" + list.size());