ArrayList In Java.
Tags: java, arraylists, 100daysofcode, algorithms
Published: 2020-09-15 05:52:03

Continuing my Blogs on [ Java ](https://www.java.com/en/) Data Structures, The next topic is [ ArrayLists  ](https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html) . So, Let's know about ArrayLists and how it essentially works. 


`ArrayList` is another tool in Java to store a large number of values that are of the same type.
In a high-level context,  
> 
They are a dynamic-array implementation of  [List ](https://docs.oracle.com/javase/7/docs/api/java/util/List.html) Interface.

So when we create an ArrayList, And we add or remove elements from the list, It automatically changes the size of the array by itself, that is what a dynamic array means.

ArrayList contains various methods for adding, removing, and retrieving elements from a List.
So let's first see how to declare an ArrayList.

```
import java.util.ArrayList;

public class ArrayListEx{
            public static void main(String[] args){
                ArrayList<String> names = new ArrayList<>();                     
       }
}
``` 
So in the above code, we import the ArrayList first by  `java.util.ArrayList` and then we declare the ArrayList  by `ArrayList<String> names = new ArrayList<>(); ` which creates a list called names which is of type **String**. 

The general syntax is:-
```
ArrayList<Type> list = new ArrayList<>();
``` 
Type is basically the type of values stored in the list such as Integer, Boolean, Double, etc.

### Adding, Removing, and Retrieving values from the ArrayList.

To **Add** value into an Arraylist, we use the `add()` method. Let's see it by example.


```
import java.util.ArrayList;

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

            ArrayList<String> namesList = new ArrayList<String>();  //Creates a ArrayList of name "namesList"
            namesList.add("Tarun");   
            namesList.add("Jim");
            namesList.add("John");
            System.out.println("The List is: "+namesList);    //prints the list

           /*Output:
              The List is: [Tarun, Jim, John]
           */
}
}
``` 

We can add value in the list at a particular `index`, That is by mentioning the index value first and then the element next in the add method. Below is an example of that:-


```
// Note: Using the same list as above
      namesList.add(1,"Jake");   
//So now the ArrayList contains another value at index 1.
      System.out.println(namesList);

    //The Output is : [Tarun, Jake, Jim, John]
``` 

To **retrieve** a value from the ArrayList we use the `get()` method. To retrieve an element at index 2 in the "namesList" ArrayList we use `namesList.get(2)`.


```
    System.out.println(namesList.get(2));   // Prints the element at index 2.
    // Output :  Jim
``` 

And To **remove** elements from an ArrayList, we use the `remove()` method. We can remove an element by giving the index or by the value itself as the parameter.
Let's see an example.

```
    namesList.remove("Jim");  //Removing the String Jim 
    namesList.remove(1);  //Removing the value at index 1
    System.out.println(namesList);

//Output : [Tarun, John]
``` 
Of course, these aren't the only methods in the ArrayList but they are the most used ones. There are many methods such as the `clear()` method, which removes all the elements from the list. `contains()` method, which checks if the given element is in the list.

If you wish to explore other methods, You can visit the official [ Documentation](https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html).

Hope you got a basic understanding of what an `ArrayList` is and how it works. 

See you in the next article and until then, Happy Coding 🙂⚡️.