Java -LinkedList class

• Java LinkedList class uses doubly linked list to store the elements. It extends the AbstractList class and implements List and Deque interfaces.
• LinkedList is a doubly-linked list implementation of the List and Deque interfaces
• Java LinkedList class can contain duplicate elements.
• Java LinkedList class maintains insertion order.
• Java LinkedList class is non synchronized.
• In Java LinkedList class, manipulation is fast because no shifting needs to be occurred.
• It doesn’t support random access for retrieving values.
• It can be used as list, stack or queue.

 

class LinkedList<E>

We can create LinkedList for storing String type elements as follows:

LinkedList<String> ll=new LinkedList<String> () ;

We can create LinkedList for Integer String type elements as follows:

LinkedList<Integer > ll=new LinkedList<Integer > () ;

Constructors of LinkedList  class as show below:

• LinkedList( )  : This constructor builds an empty linked list.
• LnkedList(Collection c) :This constructor builds a linked list that is initialized with the elements of the collection c.

 

Methods of LinkedList class:

LinkedList<String> llistobj  = new LinkedList<String>();

1) boolean add(Object item): It appends the specified element to the end of this list.

llistobj.add("A");

2) void add(int index, Object item): Inserts the specified element at the specified position(index-1) in this list.

llistobj.add(2, "B");

3) boolean addAll(Collection c): Appends all of the elements in the specified collection to the end of this list. Consider the below example –

LinkedList<String> llistobj = new LinkedList<String>();
ArrayList<String> arraylistobj= new ArrayList<String>();
arraylistobj.add("A");
arraylistobj.add("B");
llistobj.addAll(arraylistobj);

Add all the elements of ArrayList to the LinkedList.

4) boolean addAll(int index, Collection c):Inserts all of the elements in the specified collection at the specified position(index-1) into this list.

llistobj.add(2, arraylist);

5) void addFirst(Object item): It adds the item (or element) at the first position in the list.

llistobj.addFirst("A");

6) void addLast(Object item): Appends the specified element to the end of this list.

llistobj.addLast("A");

7) void clear(): It removes all the elements of a list.

llistobj.clear();

 

8) boolean contains(Object item): Returns true if this list contains the specified element otherwise false.

boolean var = llistobj.contains("hello");

9) Object clone(): It returns the copy of the list.

For e.g. My linkedList has five items: A, B, C ,D.and E

Object obj= llistobj.clone();
 System.out.println(obj);

Output: The output of above code would be:

[A, B, C, D,E]

10) int indexOf(Object item): Returns the index of the first occurrence of the specified element in this list, or return  -1 if this list does not contain the element.

llistobj.indexOf("hello");

11) int lastIndexOf(Object item): It returns the index of last occurrence of the specified element in this list, or return  -1 if this list does not contain the element .

int index= llistobj.lastIndexOf("hello);

12) Object get(int index): It returns the item of the specified index from the list.

Object var = llistobj.get(2);

13) Object getFirst(): Returns the first element in this list. Throws NoSuchElementException if this list is empty.

Object var = llistobj.getFirst();

14) Object getLast(): Returns the last element in this list. Throws NoSuchElementException if this list is empty.

Object var= llistobj.getLast();

 

15) Object poll(): It returns and removes the first item of the list.

Object obj = llistobj.poll();

16) Object pollFirst(): Retrieves and removes the first element of this list, or returns null if this list is empty.

Object obj = llistobj.pollFirst();

17) Object pollLast(): Retrieves and removes the last element of this list, or returns null if this list is empty.

Object obj = llistobj.pollLast();

18) Object remove(): It removes the first element of the list.

llistobj.remove();

19) Object remove(int index): It removes the item from the list which is present at the specified index.

llistobj.remove(2);

20) Object remove(Object obj): Removes the first occurrence of the specified element from this list, if it is present.

llistobj.remove("A");

21) Object removeFirst(): It removes the first element from the list.

llistobj.removeFirst();

22) Object removeLast(): It removes the last element of the list.

llistobj.removeLast();

23) Object removeFirstOccurrence(Object item): It removes the first occurrence of the specified item.

llistobj.removeFirstOccurrence("A");

24) Object removeLastOccurrence(Object item): It removes the last occurrence of the given element.

llistobj.removeLastOccurrence("A);

25) Object set(int index, Object item): Replaces the element at the specified index in this list with the specified element. Throws IndexOutOfBoundsException if the specified index is is out of range.

llistobj.set(1, "A");

26) int size(): It returns the number of elements of the list.

llistobj.size();

Example of LinkedList in Java

import java.util.Iterator;

import java.util.LinkedList;

 

public class MyLinkedListDemo {

 

    public static void main(String a[]){

        LinkedList<String> arrl = new LinkedList<String>();

        //adding elements to the end

        arrl.add("A");

        arrl.add("B");

        arrl.add("C");

        arrl.add("D");

        Iterator<String> itr = arrl.iterator();

        while(itr.hasNext()){

            System.out.println(itr.next());

        }

    }

}

Output:

A
B
C
D

Download this example from Here

 Another Example of LinkedList in Java

Example for copying  ArrayList into at the end  of LinkedList.

import java.util.ArrayList;

import java.util.LinkedList;

import java.util.List;

 

public class MyLinkedListDemo1 {

 

    public static void main(String a[]){

         

        LinkedList<String> listobj= new LinkedList<String>();

        //adding elements to the end

        arrl.add("A");

        arrl.add("B");

        arrl.add("C");

        arrl.add("D");

        System.out.println("Actual LinkedList:"+arrl);

        List<String> list = new ArrayList<String>();

        list.add("one");

        list.add("two");

        listobj.addAll(list); //copy at end of actual linkedlist

        System.out.println("After Copy LinkedList: "+listobj);

    }

}

Output:

Actual LinkedList:[A, B, C, D] 
After Copy LinkedList : [A, B, C, D, one, two] 

Download this example from Here