How to remove all elements of ArrayList in Java?

In Java, the ArrayList class provides various built-in methods to remove all or a single element from it.

Once those methods are called on the ArrayList, the list will become empty (). You can verify this using the size() method; it returns 0, if the list is empty.

We can remove all the elements of an ArrayList in Java:

• Using clear() Method of List Interface
• Using removeAll() Method

Removing all ArrayList Elements using clear() Method

The clear() method of the List interface removes (deletes) all the elements from a list. Once this method is called on a specific list (or an ArrayList), the list will become empty ().

Following is the syntax of the clear() method:

clear()

Example

In the following example, we use the clear() method to remove all elements from the ArrayList {10, 20, 30, 40}:

import java.util.ArrayList;

public class removeElements {
   public static void main(String[] args) {
   
      //creating an ArrayList
      ArrayList<Integer> list = new ArrayList<>();
      
      //adding element to it, which will be remove later
      list.add(10);
      list.add(20);
      list.add(30);
      list.add(40);
      
      System.out.println("The ArrayList is: " + list);
      
      //using clear() method
      list.clear();
      System.out.println("ArrayList after removing all elements: " + list);
   }
}

Following is the output of the above program:

The ArrayList is: [10, 20, 30, 40]
ArrayList after removing all elements: []

Using the removeAll() Method

The removeAll() method of the List interface accepts a collection as a parameter, and it removes all elements of the current list that (also) exist in the given collection.

If we use the ArrayList object, invoke this method and pass the same as a parameter to it, all the elements from the ArrayList will be removed. Following is the syntax of the removeAll() method:

boolean removeAll(Collection<?> c)

Here, c is a collection containing elements to be removed from the list.

Example

In this example, we use the removeAll() method to remove all ArrayList elements that are specified within the same list:

import java.util.ArrayList;

public class removeElements {
   public static void main(String[] args) {
   
      //creating an ArrayList
      ArrayList<Integer> list = new ArrayList<>();
      
      //adding element to it, which will be remove later
      list.add(1);
      list.add(2);
      list.add(3);
      list.add(4);
      
      System.out.println("The ArrayList is: " + list);
      
      //using removeAll() method to remove all ArrayList elements
      list.removeAll(list);
      System.out.println("ArrayList after removing all elements: " + list);
   }
}

The above program produces the following output:

The ArrayList is: [1, 2, 3, 4]
ArrayList after removing all elements: []