You can use the Java List interface to store objects/elements in an ordered collection. It extends the Collection interface.

The  List interface provides us with various methods for inserting, accessing, and deleting elements in a collection.  

In this article, you'll learn how to extend and implement the List interface in Java, and how to interact with elements in a collection.

Implementation Classes of the Java List Interface

Here are the different implementation classes of the List interface in Java:

  • AbstractList.
  • AbstractSequentialList.
  • ArrayList.
  • AttributeList.
  • CopyOnWriteArrayList.
  • LinkedList.
  • RoleList.
  • RoleUnresolvedList.
  • Stack.
  • Vector.

The most commonly used implementation of the List interface are ArrayList and LinkedList.

Since both classes above implement the List interface, they make use of the same methods to add, access, update, and remove elements in a collection.

In this tutorial, we'll have a look at how we can add, access, update, and remove elements in a collection using the ArrayList.

How to Implement a List in Java Using ArrayList

Unlike arrays in Java, which have a specified size, the ArrayList is more dynamic when it comes to storing elements. This means that you can add items as you please.

Here's how you can create an ArrayList:

import java.util.ArrayList;

public class Main {
    
  public static void main(String[] args) {
      
    ArrayList<String> students = new ArrayList<String>();
    
  }
}

In the code above, we first imported the ArrayList class: import java.util.ArrayList;.

We then created a new ArrayList object called students: ArrayList<String> students = new ArrayList<String>();.

Note that the data types of elements that would be stored in the ArrayList were specified in angle brackets: <String>.

How to Add Elements to the ArrayList

You can use the add() method to add elements to the ArrayList.

Here's an example:

import java.util.ArrayList;

public class Main {
    
  public static void main(String[] args) {
      
    ArrayList<String> students = new ArrayList<String>();
    
    
    students.add("John");
    students.add("Jane");
    students.add("Doe");
    
    
    System.out.println(students);
    // [John, Jane, Doe]
    
  }
}

In the code above, we passed the element to be added to the ArrayList as a parameter: students.add("Doe").

How to Access Elements in the ArrayList

To access elements in the ArrayList, you make use of the get() method. Here's how:

import java.util.ArrayList;

public class Main {
    
  public static void main(String[] args) {
      
    ArrayList<String> students = new ArrayList<String>();
    
    
    students.add("John");
    students.add("Jane");
    students.add("Doe");
    
    System.out.println(students.get(1));
    // Jane
    
  }
}

As can be seen above, we passed in the index of the element to be accessed as a parameter to the get() method: students.get(1).

How to Update Elements in the ArrayList

To update the value of elements in the ArrayList, you make use of the set() method.

It takes two parameters: the index of the element to be updated, and the new value.

Here's an example:

import java.util.ArrayList;

public class Main {
    
  public static void main(String[] args) {
      
    ArrayList<String> students = new ArrayList<String>();
    
    
    students.add("John");
    students.add("Jane");
    students.add("Doe");
    
    students.set(2,"Jade");
    
    System.out.println(students);
    // [John, Jane, Jade]
    
  }
}

How to Remove Elements in the ArrayList

To remove elements in the ArrayList, you make use of the remove() method. We also use the index to specify which element to remove. 

import java.util.ArrayList;

public class Main {
    
  public static void main(String[] args) {
      
    ArrayList<String> students = new ArrayList<String>();
    
    
    students.add("John");
    students.add("Jane");
    students.add("Doe");
    
    students.remove(2);
    
    System.out.println(students);
    // [John, Jane]
    
  }
}

You can use the clear() method to remove all the elements in the collection:

import java.util.ArrayList;

public class Main {
    
  public static void main(String[] args) {
      
    ArrayList<String> students = new ArrayList<String>();
    
    students.add("John");
    students.add("Jane");
    students.add("Doe");
    
    students.clear();
    
    System.out.println(students);
    // []
    
  }
}

Although the ArrayList and LinkedList classes both have the same methods as seen in the examples in this article, the LinkedList class has some additional methods like:

  • addFirst() adds an element at the beginning of the list.
  • addLast() adds an element at the end of the list.
  • getFirst() returns the first element of the list.
  • getLast() returns the last element of the list.
  • removeFirst() removes the first element of the list.
  • removeLast() removes the last element of the list.

Summary

In this article, we talked about the List interface in Java. You use it to store ordered collections of elements.

We had a look at some of the implementation classes of the List interface. The most commonly used are the ArrayList and LinkedList classes.

Using code examples, we saw how to add, access, update, and remove elements in a collection with the ArrayList.

Although both ArrayList and LinkedList have similar methods, we highlighted some of the additional methods that you can use with the LinkedList class.

Happy coding!