Java LinkedList

LinkedList in java is a resizable array like ArrayList. There is no size limit in LinkedList. When you add new elements or items in the LinkedList, the size or capacity of LinkedList will grow. You can do many things like add new elements, remove elements, change elements, sort the elements etc. like ArrayList. Both ArrayList and LinkedList implements List interface. Thus, possibly all the methods you can use in the ArrayList can also be used in LinkedList.

Additionally, LinkedList provides additional methods to manipulate your data.

# Methods for LinkedList:

# Creating LinkedList

Syntax:

Non generic:

LinkedList list = new LinkedList();

Generic approach: (with wrapper types)

LinkedList list = new LinkedList(); 

//T stands for type but wrapper. Primitive is not supported.

//such as 
LinkedList list = new LinkedList(); 

Below is a simple example, where we created a LinkedList object and add String data using add() method.

public class Main{
  public static void main (String[] args){
    //creating LinkedList
    LinkedList fruits = new LinkedList(); 
    //add new elements
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry")
    fruits.add("Guava");
    fruits.add("Blackberry");
    
    //print the elements
    System.out.println(fruits);
  }
}

/**
 * Output: 
 * [Apple, Banana, Cherry, Guava, Blackberr]
 */

# Removing elements from the LinkedList

import java.util.LinkedList;
 
 public class Main{
  public static void main (String[] args){
    //creating LinkedList
    LinkedList fruits = new LinkedList(); 
    //add new elements
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry");
    fruits.add("Guava");
    fruits.add("Blackberry");
    
    //print the elements
    System.out.println(fruits);
    
    //remove the first element
    fruits.remove("Apple");
    //Now print the above fruits list
    System.out.println(fruits);
  }
}

/**
 * Output: 
 * [Apple, Banana, Cherry, Guava, Blackberr]
 * After removing
 * [Banana, Cherry, Guava, Blackberry]
 */

Note: remove(0) also works the same. One is based on element and other one is position.

# Change an LinkedList element using set() method

import java.util.ArrayList;

public class Main{
  public static void main (String[] args){
    LinkedList fruits = new LinkedList();

    //add elements using add method
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry");
    fruits.add("Guava");
    fruits.add("Plum");
 
    //iterating LinkedList elements
    System.out.println("Before Changing");
    for(String f: fruits){
      System.out.println(f);
    }
    
    //change the fruits and then iterate
    System.out.println("After changing");
    fruits.set(0, "Blueberry");
    //iterate now 
    for(String f: fruits){
      System.out.println(f);
    }
  }
}

If you run the above program, you will get the following output in the console. You can see, the first fruit element has been updated.

Before Changing
Apple
Banana
Cherry
Guava
Plum
After changing
Blueberry
Banana
Cherry
Guava
Plum

Note: The add(int index, element) and set(int index, element) can be used interchangeably

# Iterate LinkedList elements

# For iterating LinkedList elements we can use java for loop.

import java.util.LinkedList;

public class Main{
  public static void main (String[] args){
    LinkedList fruits = new LinkedList();
    //add elements using add method
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry");
    fruits.add("Guava");
    fruits.add("Plum");
    
    //iterate
    for(int i = 0; i <=fruits.size(); i++){
      System.out.println(fruits.get(i));
    }
  }
}

If you run the above example you get the following output:

Apple Banana Cherry Guava Plum

# Iterating LinkedList elements using for each loop.

import java.util.LinkedList;

public class Main{
  public static void main (String[] args){
    LinkedList fruits = new LinkedList();
    //add elements using add method
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry");
    fruits.add("Guava");
    fruits.add("Plum");
    
    //iterate and print 
    for(String f: fruits){
      System.out.println(f);
    }
  }
}
/**
 * Apple
 * Banana
 * Cherry
 * Guava
 * Plum
 */

# Iterating LinkedList using Iterator

import java.util.LinkedList;
import java.util.Iterator;
//import all the classes 
//import java.util.*;
 
 public class Main{
   public static void main (String[] args) {
     //Creating ArrayList
     LinkedList fruits = new LinkedList();
     //add elements to this ArrayList
     fruits.add("Apple");
     fruits.add("Banana");
     fruits.add("Cherry");
     fruits.add("Guava");
     fruits.add("Plum");
     
     //iterate using Iterator
     Iterator list = fruits.iterator(); //getting Iterator
     while(list.hasNext()){ //check if any elements exists or not
       System.out.println(list.next()); //printing the elements 
     }
   }
 }
 
/**
 * Apple
 * Banana
 * Cherry
 * Guava
 * Plum
 */

# Using addFirst(), addLast(), removeFast(), removeLast() methods in LinkedList

import java.util.LinkedList;
 
 public class Main{
  public static void main (String[] args){
    //creating LinkedList
    LinkedList fruits = new LinkedList(); 
    //add new elements
    fruits.add("Apple");
    fruits.add("Banana");
    fruits.add("Cherry");
    fruits.add("Guava");
    fruits.add("Blackberry");
    
    //print the elements
    System.out.println(fruits);
    
    //addFirst() 
    fruits.addFirst("Orange");
    
    //Now print the above fruits list
    System.out.println(fruits);
    
   //addLast() 
   fruits.addLast("Plum")
   //now print fruits
   System.out.println(fruits);
   
   //removeFast()
   fruits.removeFirst();
   //print the list
   System.out.println(fruits);
   
   //removeLast()
   fruits.removeLast();
   //print the list now
   System.out.println(fruits);
  }
}

After running the above program, you will get the following output. Now think, what's going on here?

[Apple, Banana, Cherry, Guava, Blackberry]
[Orange, Apple, Banana, Cherry, Guava, Blackberry]
[Orange, Apple, Banana, Cherry, Guava, Blackberry, Plum]
[Apple, Banana, Cherry, Guava, Blackberry, Plum]
[Apple, Banana, Cherry, Guava, Blackberry]