LinkedList in Java

In Java, LinkedList is a class that implements the List interface and provides a way to store a collection of elements as a linked list. In this answer, I will explain how to use LinkedList in Java, as well as some of its commonly used methods.

Creating a LinkedList

To use LinkedList in Java, you must first import the java.util.LinkedList class. You can create a new LinkedList by instantiating the class with a type parameter that specifies the type of elements the list will hold. Here’s an example of how to create a new LinkedList that can hold elements of type String:

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

Adding and Removing Elements

Once a LinkedList has been created, elements can be added or removed from it using the following methods:

// Add an element to the end of the list
list.add("apple");

// Add an element at the specified index
list.add(1, "banana");

// Remove an element at the specified index
String removed = list.remove(0);

// Remove the first occurrence of an element
boolean success = list.remove("banana");

// Remove and return the first element in the list
String first = list.removeFirst();

// Remove and return the last element in the list
String last = list.removeLast();

// Return the first element in the list without removing it
first = list.peekFirst();

// Return the last element in the list without removing it
last = list.peekLast();

// Remove all elements from the list
list.clear();

Accessing Elements

LinkedList provides several methods to access elements in the list:

// Get the number of elements in the list
int size = list.size();

// Check if the list is empty
boolean isEmpty = list.isEmpty();

// Get the element at the specified index
String element = list.get(1);

// Set the element at the specified index
list.set(1, "cherry");

// Convert the list to an array
String[] array = list.toArray(new String[0]);

// Iterate over the elements in the list using a for-each loop
for (String element : list) {
    System.out.println(element);
}

Other Commonly Used Methods

Some other commonly used methods provided by the LinkedList class include:

// Add an element to the front of the list
list.addFirst("date");

// Add an element to the end of the list
list.addLast("elderberry");

// Get the first element in the list
first = list.getFirst();

// Get the last element in the list
last = list.getLast();

// Remove and return the first element in the list, returns null if the list is empty
first = list.poll();

// Remove and return the first element in the list, throws an exception if the list is empty
first = list.remove();

One important thing to keep in mind when using a LinkedList is that it provides a way to store elements as a linked list, which can be useful for certain types of algorithms. However, because it uses a linked list, it can be slower than other types of collections for random access to elements, such as when using the get() method. It’s important to understand the behavior of the methods you are using and how they may affect the performance of your code.