How to Iterate LinkedList in Java?

LinkedList in java is basically a part of the collection framework present in java.util package. It is the implementation of the LinkedList data structure that stores elements in a non-contiguous manner inside the memory.

Five ways to iterate a LinkedList are:

1. Using for loop
2. Using while loop
3. Using enhanced for loop
4. Using Iterator
5. Using forEach() method

Method 1: Using For Loop

Java

// Java program for iterating the LinkedList
// using For loop

import java.util.LinkedList;

public class GFG {
    public static void main(String[] args)
    {

        // Creating a LinkedList of Integer type
        LinkedList<Integer> linkedList = new LinkedList<>();

        // Inserting some Integer values to our LinkedList
        linkedList.add(40);
        linkedList.add(44);
        linkedList.add(80);
        linkedList.add(9);

        // LinkedList after insertions: [40, 44, 80, 9]

        // Calling the function to iterate our LinkedList
        iterateUsingForLoop(linkedList);
    }

    // Function to iterate the LinkedList using a simple for
    // loop
    public static void
             iterateUsingForLoop(LinkedList<Integer> linkedList)
    {

        System.out.print(
            "Iterating the LinkedList using a simple for loop : ");

        for (int i = 0; i < linkedList.size(); i++) {
            System.out.print(linkedList.get(i) + " ");
        }
    }
}

Output

Iterating the LinkedList using a simple for loop : 40 44 80 9

Method 2: Using while Loop

We can iterate our LinkedList using a while loop in a very similar way as we did using a for loop.

Java

// Java program for iterating the LinkedList
// using while loop

import java.util.LinkedList;

public class GFG {
    public static void main(String[] args) {

        // Creating a LinkedList of Character type
        LinkedList<Character> vowels = new LinkedList<>();

        // Inserting some Character values to our LinkedList
        vowels.add('a');
        vowels.add('e');
        vowels.add('i');
        vowels.add('o');
        vowels.add('u');

        // LinkedList after insertions: ['a', 'e', 'i', 'o', 'u']

        // calling the function to iterate our LinkedList
        iterateUsingWhileLoop(vowels);
    }

    // Function to iterate our LinkedList using while loop
    public static void iterateUsingWhileLoop(LinkedList<Character> vowels){

        System.out.print("Iterating the LinkedList using while loop : ");

        int i=0;

        while(i<vowels.size()){
            System.out.print(vowels.get(i) + " ");
            i++;
        }

    }
}

Output

Iterating the LinkedList using while loop : a e i o u

Method 3: Using enhanced for loop

Using enhanced for loop we can sequentially iterate a LinkedList. The execution of the enhanced for loop ends after we visit all the elements. Let us see an example of iterating the LinkedList using the enhanced for loop.

Java

// Java program for iterating the LinkedList
// using Enhanced For loop

import java.util.LinkedList;

public class GFG {
    public static void main(String[] args)
    {

        // Creating a LinkedList of String type
        LinkedList<String> linkedList = new LinkedList<>();

        // Inserting some String values to our LinkedList
        linkedList.add("Geeks");
        linkedList.add("for");
        linkedList.add("Geeks");

        // LinkedList after insertions: ["Geeks", "for",
        // "Geeks]

        // Calling the function to iterate our LinkedList
        iterateUsingEnhancedForLoop(linkedList);
    }

    // Function to display LinkedList using Enhanced for
    // loop
    public static void iterateUsingEnhancedForLoop(LinkedList<String> linkedList)
    {

        System.out.print(
            "Iterating the LinkedList using enhanced for loop : ");

        for (String listElement : linkedList) {
            System.out.print(listElement + " ");
        }
    }
}

Output

Iterating the LinkedList using enhanced for loop : Geeks for Geeks

Method 4: Using Iterator

• To iterate the LinkedList using the iterator we first create an iterator to the current list and keep on printing the next element using the next() method until the next element exists inside the LinkedList.
• We check if the LinkedList contains the next element using the hasNext() method.

Java

// Java program for iterating the LinkedList
// using Iterator

import java.util.Iterator;

// Importing LinkedList class from
// java.util package
import java.util.LinkedList;

public class GFG {
    public static void main(String[] args) {

        // Creating a LinkedList of Integer Type
        LinkedList<Integer> linkedList = new LinkedList<>();

        // Inserting some Integer values to our LinkedList
        linkedList.add(5);
        linkedList.add(100);
        linkedList.add(41);
        linkedList.add(40);
        linkedList.add(7);

        // LinkedList after insertions : [5, 100, 41, 40, 7]

        // Calling the function to iterate our LinkedList
        iterateUsingIterator(linkedList);
    }

    // Function to iterate the Linked List using Iterator
    public static void iterateUsingIterator(LinkedList<Integer> linkedList){

        System.out.print("Iterating the LinkedList using Iterator : ");

        // Creating an Iterator to our current LinkedList
        Iterator it = linkedList.iterator();

        // Inside the while loop we check if the next element
        // exists or not if the next element exists then we print
        // the next element and move to it otherwise we come out
        // of the loop

        // hasNext() method return boolean value
          // It returns true when the next element
          // exists otherwise returns false
        while(it.hasNext()){

            // next() return the next element in the iteration
            System.out.print(it.next() + " ");
        }

    }
}

Output

Iterating the LinkedList using Iterator : 5 100 41 40 7

Method 5: Using forEach() method

• forEach() method was introduced in Java8. 
• It performs the specified task for each element of the Iterable until all elements have been processed or the action throws an exception. 

Syntax: 

public void forEach(Consumer<? super E> action)

Java

// Java program for iterating the LinkedList
// using For Each loop

import java.util.LinkedList;

public class GFG {
    public static void main(String[] args)
    {

        // Creating a LinkedList of Integer Type
        LinkedList<Integer> linkedList = new LinkedList<>();

        // Inserting some Integer values to our LinkedList
        linkedList.add(1);
        linkedList.add(2);
        linkedList.add(3);
        linkedList.add(4);
        linkedList.add(5);

        // LinkedList after insertions: [1, 2, 3, 4, 5]

        // Calling the function to iterate our LinkedList
        iterateUsingForEach(linkedList);
    }

    public static void
            iterateUsingForEach(LinkedList<Integer> linkedList)
    {

        System.out.print(
            "Iterating the LinkedList using for each function : ");

        // Calling the forEach function to iterate through
        // all the elements inside the Linked List
        linkedList.forEach(
            (element) -> System.out.print(element + " "));
    }
}

Output

Iterating the LinkedList using for each function : 1 2 3 4 5