Java .removeAll()

The .removeAll() method is used for removing multiple elements from instances of the ArrayList class.

Syntax

  ArrayList1.removeAll(ArrayList2);

• ArrayList1: It is the ArrayList from which elements will be removed.
• ArrayList2: It is the ArrayList containing the elements to be removed from ArrayList1.

Example

In the example below, two ArrayList instances, fallMonths and monthsToRemove, are created to hold String type elements. Elements are added to the fallMonths using the [.add()] (https://www.codecademy.com/resources/docs/java/array-list/add) method. Then, monthsToRemove is utilized to remove the months - August and September from fallMonths using .removeAll(). Finally, all elements are removed from fallMonths by invoking .removeAll() with a reference to itself.

import java.util.ArrayList;

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

    ArrayList<String> fallMonths = new ArrayList<String>();

    fallMonths.add("August");
    fallMonths.add("September");
    fallMonths.add("October");
    fallMonths.add("November");
    fallMonths.add("December");

    ArrayList<String> monthsToRemove = new ArrayList<String>();

    monthsToRemove.add("August");
    monthsToRemove.add("December");

    // Remove August and December from fallMonths using monthsToRemove
    fallMonths.removeAll(monthsToRemove);

    System.out.println("After removing specified months: " + fallMonths);

    // Remove all elements from fallMonths
    fallMonths.removeAll(fallMonths);

System.out.println("After removing all elements: " + fallMonths);
  }
}

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The output of the above code should look like this:

After removing specified months: [September, October, November]
After removing all elements: []

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