Java LinkedList Collection

What is LinkedList Collection in java?

• LinkedList class is one of the collection class in java.
• LinkedList class extends AbstractSequentialList and implements the List interface.
• LinkedList class provides a linked list data structure.

LinkedList Constructors Types

LinkedList()

This constructor builds an empty linked list.

LinkedList(Collection collection)

This constructor builds an linked list that is initialized with the elements of the collection.

LinkedList Methods

• addFirst method is used to add new object to the start of linked list.

  void addFirst(Object)
  

• addLast method is used to add new object to the end of linked list.

  void addLast(Object)
  

• getFirst method is used to get the first element in the linked list.

  Object getFirst()
  

• getLast method is used to get the last element in the linked list.

  Object getLast()
  

• removeFirst method is used to remove fist element in the linked list.

  Object removeFirst()
  

• removeLast method is used to remove last element in the linked list.

  Object removeLast()
  

• LinkedList implements List interface, so add method is also can be used to add new object in the end of linked list.

  boolean add(Object)
  

  adds new object at end of the array list.

  boolean add(int, Object)
  

  adds new object at the specified index of array list.
• get method is used to get the element based on index.

  Object get(int index)
  

• set method is used to set the element using index.

  void set(int index, Object obj)
  

Creating LinkedList and Adding Elements in Java Program

// Codingpointer Demonstrates LinkedList                                        
                                                                                
import java.util.*;                                                             
                                                                                
class LinkedListTest {                                                          
 public static void main(String args[]) {                                       
  // Creates LinkedList                                                         
  LinkedList ll = new LinkedList();                                             
                                                                                
  // add linked list elements.                                                  
  ll.add(new Integer(5));                                                       
  ll.add(new Integer(1));                                                       
  ll.add(new Integer(3));                                                       
  ll.add(new Integer(2));                                                       
  ll.add(new Integer(4));                                                       
  ll.addFirst("start");                                                         
  ll.addLast("end");                                                            
  ll.add(2, "insert");                                                          
                                                                                
  System.out.println("Size of Linked list: "+ ll.size());                       
  // prints linked list elements                                                
  System.out.println("Elements in linked list: " + ll);                         
 }                                                                              
}  

Output:

$ java LinkedListTest
Size of Linked list: 8
Elements in linked list: [start, 5, insert, 1, 3, 2, 4, end]

Remove Elements in LinkedList Java Program

// Codingpointer Demonstrates LinkedList                                        
                                                                                
import java.util.*;                                                             
                                                                                
class LinkedListTest {                                                          
 public static void main(String args[]) {                                       
  // Creates LinkedList                                                         
  LinkedList ll = new LinkedList();                                             
                                                                                
  // add linked list elements.                                                  
  ll.add(new Integer(5));                                                       
  ll.add(new Integer(1));                                                       
  ll.add(new Integer(3));                                                       
  ll.add(new Integer(2));                                                       
  ll.add(new Integer(4));                                                       
  ll.addFirst("start");                                                         
  ll.addLast("end");                                                            
  ll.add(2, "insert");                                                          
                                                                                
  // remove elements in linked list                                             
  ll.remove(2);                                                                 
  ll.removeFirst();                                                             
  ll.removeLast();                                                              
                                                                                
  System.out.println("Size of Linked list: "+ ll.size());                       
  // prints linked list elements                                                
  System.out.println("Elements in linked list: " + ll);                         
 }                                                                              
}     

Output:

$ java LinkedListTest
Size of Linked list: 5
Elements in linked list: [5, 1, 3, 2, 4]

LinkedList get and set methods

// Codingpointer Demonstrates LinkedList                                        
                                                                                
import java.util.*;                                                             
                                                                                
class LinkedListTest {                                                          
 public static void main(String args[]) {                                       
  // Creates LinkedList                                                         
  LinkedList ll = new LinkedList();                                             
                                                                                
  // add linked list elements.                                                  
  ll.add(new Integer(5));                                                       
  ll.add(new Integer(1));                                                       
  ll.add(new Integer(3));                                                       
  ll.add(new Integer(2));                                                       
  ll.add(new Integer(4));                                                       
  ll.addFirst("start");                                                         
  ll.addLast("end");                                                            
  ll.add(2, "insert");                                                          
                                                                                
  // get and set elements in linked list.                                       
  Object obj = ll.get(3);                                                       
  System.out.println("get value: " + obj);                                      
  ll.set(3, (obj.toString() + " changed"));                                     
                                                                                
  System.out.println("Size of Linked list: "+ ll.size());                       
  // prints linked list elements                                                
  System.out.println("Elements in linked list: " + ll);                         
 }                                                                              
}        

Output:

$ java LinkedListTest
get value: 1
Size of Linked list: 8
Elements in linked list: [start, 5, insert, 1 changed, 3, 2, 4, end]

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