Java LinkedList Tutorial

LinkedList in Java is a part of the Java Collections Framework and implements the List interface. It provides a doubly-linked list data structure that allows for efficient insertion, removal, and traversal operations, especially when operating near the head or tail of the list. Here, we’ll explore LinkedList through various examples to demonstrate its usage and benefits.

Basic Operations

Creating a LinkedList

import java.util.LinkedList;

public class LinkedListExample {
    public static void main(String[] args) {
        LinkedList<String> animals = new LinkedList<>();
        animals.add("Dog");
        animals.add("Cat");
        animals.add("Horse");

        System.out.println(animals); // Output: [Dog, Cat, Horse]
    }
}

import java.util.LinkedList;

public class LinkedListExample {

public static void main(String[] args) {

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

animals.add("Dog");

animals.add("Cat");

animals.add("Horse");

System.out.println(animals); // Output: [Dog, Cat, Horse]

}

Adding Elements

Elements can be added at the beginning, end, or any position within the list.

animals.addFirst("Elephant"); // Adds to the beginning
animals.addLast("Zebra"); // Adds to the end
animals.add(2, "Lion"); // Adds at index 2

System.out.println(animals); // Output: [Elephant, Dog, Lion, Cat, Horse, Zebra]

animals.addFirst("Elephant"); // Adds to the beginning

animals.addLast("Zebra"); // Adds to the end

animals.add(2, "Lion"); // Adds at index 2

System.out.println(animals); // Output: [Elephant, Dog, Lion, Cat, Horse, Zebra]

Removing Elements

Elements can be removed from the beginning, end, or a specific position.

animals.removeFirst(); // Removes the first element
animals.removeLast(); // Removes the last element
animals.remove("Lion"); // Removes the first occurrence of "Lion"

System.out.println(animals); // Output: [Dog, Cat, Horse]

animals.removeFirst(); // Removes the first element

animals.removeLast(); // Removes the last element

animals.remove("Lion"); // Removes the first occurrence of "Lion"

System.out.println(animals); // Output: [Dog, Cat, Horse]

Iterating Over a LinkedList

Using for-loop

for (int i = 0; i < animals.size(); i++) {
    System.out.println(animals.get(i));
}

for (int i = 0; i < animals.size(); i++) {

System.out.println(animals.get(i));

}

Using for-each loop

for (String animal : animals) {
    System.out.println(animal);
}

for (String animal : animals) {

System.out.println(animal);

}

Using Iterator

import java.util.Iterator;
Iterator<String> iterator = animals.iterator();
while (iterator.hasNext()) {
    System.out.println(iterator.next());
}

import java.util.Iterator;

Iterator<String> iterator = animals.iterator();

while (iterator.hasNext()) {

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

}

Other Useful Operations

Accessing Elements

String firstElement = animals.getFirst();
String lastElement = animals.getLast();
System.out.println("First: " + firstElement + ", Last: " + lastElement); // Output: First: Dog, Last: Horse

String firstElement = animals.getFirst();

String lastElement = animals.getLast();

System.out.println("First: " + firstElement + ", Last: " + lastElement); // Output: First: Dog, Last: Horse

Finding the Index of an Element

int index = animals.indexOf("Cat");
System.out.println("Index of Cat: " + index); // Output: Index of Cat: 1

1 2	int index = animals.indexOf("Cat"); System.out.println("Index of Cat: " + index); // Output: Index of Cat: 1

Converting to an Array

String[] animalsArray = animals.toArray(new String[0]);
System.out.println(Arrays.toString(animalsArray)); // Output: [Dog, Cat, Horse]

1 2	String[] animalsArray = animals.toArray(new String[0]); System.out.println(Arrays.toString(animalsArray)); // Output: [Dog, Cat, Horse]

LinkedList vs. ArrayList

While LinkedList and ArrayList both implement the List interface, the choice between them depends on the specific needs of your application.

LinkedList is generally preferred when:

Frequent addition and removal of elements are required.
You predominantly work with elements at the beginning or end of the list.

In contrast, ArrayList may be more efficient for scenarios involving:

Frequent access to list elements by their index.
Less frequent addition/removal of elements.

Conclusion

LinkedList in Java offers a flexible and efficient way to manage dynamic lists, with easy insertion and removal operations. Understanding how to utilize LinkedList, along with its strengths and weaknesses compared to other list implementations like ArrayList, is crucial for Java developers in crafting efficient and effective applications.