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Linkedlist in Java

LinkedList in Java

LinkedList is an implementation of List interface.

Example of LinkedList in Java

import java.util.*;
public class LinkedListExample {
     public static void main(String args[]) {

         /* Linked List Declaration */
         LinkedList<String> linkedlist = new LinkedList<String>();

         /*add(String Element) is used for adding 
          * the elements to the linked list*/
         linkedlist.add("Item1");
         linkedlist.add("Item5");
         linkedlist.add("Item3");
         linkedlist.add("Item6");
         linkedlist.add("Item2");

         /*Display Linked List Content*/
         System.out.println("Linked List Content: " +linkedlist);

         /*Add First and Last Element*/
         linkedlist.addFirst("First Item");
         linkedlist.addLast("Last Item");
         System.out.println("LinkedList Content after addition: " +linkedlist);

         /*This is how to get and set Values*/
         Object firstvar = linkedlist.get(0);
         System.out.println("First element: " +firstvar);
         linkedlist.set(0, "Changed first item");
         Object firstvar2 = linkedlist.get(0);
         System.out.println("First element after update by set method: " +firstvar2);

         /*Remove first and last element*/
         linkedlist.removeFirst();
         linkedlist.removeLast();
         System.out.println("LinkedList after deletion of first and last element: " +linkedlist);

         /* Add to a Position and remove from a position*/
         linkedlist.add(0, "Newly added item");
         linkedlist.remove(2);
         System.out.println("Final Content: " +linkedlist); 
     }
}
Output:
Linked List Content: [Item1, Item5, Item3, Item6, Item2]
LinkedList Content after addition: [First Item, Item1, Item5, Item3, Item6, Item2, Last Item]
First element: First Item
First element after update by set method: Changed first item
LinkedList after deletion of first and last element: [Item1, Item5, Item3, Item6, Item2]
Final Content: [Newly added item, Item1, Item3, Item6, Item2]

Methods of LinkedList class:

For all the examples in the below methods, consider llistobj as a reference for LinkedList<String>.
LinkedList<String> llistobj  = new LinkedList<String>();
1) boolean add(Object item): It adds the item at the end of the list.
llistobj.add("Hello");
It would add the string “Hello” at the end of the linked list.
2) void add(int index, Object item): It adds an item at the given index of the the list.
llistobj.add(2, "bye");
This will add the string “bye” at the 3rd position( 2 index is 3rd position as index starts with 0).
3) boolean addAll(Collection c): It adds all the elements of the specified collection c to the list. It throws NullPointerException if the specified collection is null. Consider the below example –
LinkedList<String> llistobj = new LinkedList<String>();
ArrayList<String> arraylist= new ArrayList<String>();
arraylist.add("String1");
arraylist.add("String2");
llistobj.addAll(arraylist);
This piece of code would add all the elements of ArrayList to the LinkedList.
4) boolean addAll(int index, Collection c): It adds all the elements of collection c to the list starting from a give index in the list. It throws NullPointerException if the collection c is null and IndexOutOfBoundsException when the specified index is out of the range.
llistobj.add(5, arraylist);
It would add all the elements of the ArrayList to the LinkedList starting from position 6 (index 5).
5) void addFirst(Object item): It adds the item (or element) at the first position in the list.
llistobj.addFirst("text");
It would add the string “text” at the beginning of the list.
6) void addLast(Object item): It inserts the specified item at the end of the list.
llistobj.addLast("Chaitanya");
This statement will add a string “Chaitanya” at the end position of the linked list.
7) void clear(): It removes all the elements of a list.
llistobj.clear();
8) Object clone(): It returns the copy of the list.
For e.g. My linkedList has four items: text1, text2, text3 and text4.
Object str= llistobj.clone();
 System.out.println(str);
Output: The output of above code would be:
[text1, text2, text3, text4]
9) boolean contains(Object item): It checks whether the given item is present in the list or not. If the item is present then it returns true else false.
boolean var = llistobj.contains("TestString");
It will check whether the string “TestString” exist in the list or not.
10) Object get(int index): It returns the item of the specified index from the list.
Object var = llistobj.get(2);
It will fetch the 3rd item from the list.
11) Object getFirst(): It fetches the first item from the list.
Object var = llistobj.getFirst();
12) Object getLast(): It fetches the last item from the list.
Object var= llistobj.getLast();
13) int indexOf(Object item): It returns the index of the specified item.
llistobj.indexOf("bye");
14) int lastIndexOf(Object item): It returns the index of last occurrence of the specified element.
int pos = llistobj.lastIndexOf("hello);
integer variable pos will be having the index of last occurrence of string “hello”.
15) Object poll(): It returns and removes the first item of the list.
Object o = llistobj.poll();
16) Object pollFirst(): same as poll() method. Removes the first item of the list.
Object o = llistobj.pollFirst();
17) Object pollLast(): It returns and removes the last element of the list.
Object o = 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(4);
It will remove the 5th element from the list.
20) Object remove(Object obj): It removes the specified object from the list.
llistobj.remove("Test Item");
21) Object removeFirst(): It removes the first item from the list.
llistobj.removeFirst();
22) Object removeLast(): It removes the last item of the list.
llistobj.removeLast();
23) Object removeFirstOccurrence(Object item): It removes the first occurrence of the specified item.
llistobj.removeFirstOccurrence("text");
It will remove the first occurrence of the string “text” from the list.
24) Object removeLastOccurrence(Object item): It removes the last occurrence of the given element.
llistobj.removeLastOccurrence("String1);
It will remove the last occurrence of string “String1″.
25) Object set(int index, Object item): It updates the item of specified index with the give value.
llistobj.set(2, "Test");
It will update the 3rd element with the string “Test”.
26) int size(): It returns the number of elements of the list.
llistobj.size();
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