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Linked List in Java
Understanding Linked List in Java
A linked list in Java is a linear data structure that we can use for storing a large amount of data with ease.
The data stored in Linked List is not in a contiguous manner, but each data is stored at a different location, which can be accessed according to one’s need
How to make a Linked List in Java
A linked list is a linear data structure that is made up of several nodes, which is further divided into two parts-:
- Node – This part stores the data.
- Link – This part stores the address of the memory location, where the next data of the list is stored.
Lets now have a look at Linked List implementation in Java
class LinkedList {
Node head; // head
// Linked list Node
class Node {
int data;
Node next;
// constructor to initialize
Node(int d) {
data = d;
next = null;
}
}
} Types of Linked Lists
There are many variations but below are the most important ones –
Singly Linked List
It is the most basic linked list, which is made up of several nodes, which can further be divided into two parts
- data
- next
Each node is connected to one another as the next value for each node holds the address to the next node in the sequence.
The first node is called as head and the last node is called as tail, where the last node’s next value is null.
Doubly Linked List
This is a successor of a normal linked list. Nodes of a double linked list have three parts –
- Data – Data / Value held
- Next – Reference Address to the previous node
- Next – Reference Address to next node
The main advantage is we can traverse in any direction forwards and backwards.
Circular Linked List
It is very similar to Singly Linked List with one change that rather than the last node pointing to null. It has the address to the first (head) node.
Which makes it circular in Nature, it is used in OS to implement round robin scheduling algorithms too.
Insertion and Deletion in Linked List in Java
Runimport java.lang.*; class LinkedList { Node head; // not using parameterized constructor would by default // force head instance to become null // Node head = null; // can also do this, but not required // Node Class class Node{ int data; Node next; Node(int x) // parameterized constructor { data = x; next = null; } } public Node insert(int data) { // Creating newNode memory & assigning data value Node newNode = new Node(data); // assigning this newNode's next as current head node newNode.next = head; // re-assigning head to this newNode head = newNode; return head; } public void display() { Node node = head; //as linked list will end when Node reaches Null while(node!=null) { System.out.print(node.data + " "); node = node.next; } System.out.println(""); } public void delete() { if (head == null){ System.out.println("List is empty, not possible to delete"); return; } System.out.println("Deleted: " + head.data); // move head to next node head = head.next; } } class Main{ public static void main(String args[]) { LinkedList ll = new LinkedList(); ll.insert(6); ll.insert(5); ll.insert(3); ll.insert(4); ll.insert(2); ll.insert(1); ll.display(); ll.delete(); ll.delete(); ll.display(); } }
Output
1 2 4 3 5 6 Deleted: 1 Deleted: 2 4 3 5 6
Runimport java.lang.*; // Node Class class Node { int data; Node next; Node(int x) // parameterized constructor { data = x; next = null; } } class Main { static Node insertStart(Node head, int data) { // Creating newNode memory & assigning data value Node newNode = new Node(data); // assigning this newNode's next as current head node newNode.next = head; // re-assigning head to this newNode head = newNode; return head; } public static Node delete(Node head) { if (head == null){ System.out.println("List is empty, not possible to delete"); return head; } System.out.println("Deleted: " + head.data); // move head to next node head = head.next; return head; } static void display(Node node) { //as linked list will end when Node is Null while (node != null) { System.out.print(node.data + " "); node = node.next; } System.out.println("\n"); } public static void main(String args[]) { Node head = null; head = insertStart(head,6); head = insertStart(head,5); head = insertStart(head,4); head = insertStart(head,3); head = insertStart(head,2); head = insertStart(head,1); display(head); head = delete(head); head = delete(head); display(head); } }
Output
1 2 3 4 5 6 Deleted: 1 Deleted: 2 3 4 5 6
Linked List as a part of Collection
There are various different frameworks in Java which we can use for storing and operating efficiently on our data. Such is a framework known as Collection framework in Java. In this framework there are various different classes and interfaces are present using which we can code Linked List in Java in a very easy manner as it has a pre-defined class LinkedList stored in it, which has functions like- add()
- delete()
- search()
- reverse(), etc
Linked List VS Array
| Linked List | Array |
|---|---|
| Operation like insertion and deletion are easier. | Operation like searching and traversing are easier. |
| Data is stored in a continuous manner. | Data is stored in a contiguous manner. |
| No need for pre-allocating the size of the list. | User need to define the size before inserting the data. |
| Memory loss is comparatively low. | Memory loss is comparatively high. |
Some of the pre-defined function of LinkedList class
| Method Name | Method Description |
|---|---|
| void addFirst(E e) | This method inserts an element at the beginning of the list |
| void addLast(E e) | This method inserts an element at the end of the list |
| void add(int index, E element) | This method inserts an element at the specific position of the list |
| void clear() | It is used to clear all the elements from the list |
| boolean contains(Object o) | This method returns true if the specific element is present in the list, otherwise return false |
| element() | This element let us view the first element of the list |
| getLast () | This method gives us the last element of the list |
| lastIndexOf(Object o) | This method returns the index of the last occurrence of a specified element |
| size() | This method returns the size of the list |
| toArray() | This method converts the list into an array |
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