What is the CopyOnWriteArraySet.removeAll method in Java?

The removeAll() method removes all the elements of the passed collection from the CopyOnWriteArraySet if present.

CopyOnWriteArraySet is a thread-safe version of SetA collection that contains no duplicate elements.. It internally uses CopyOnWriteArrayList for its operations. For all the write operations like add, set, etc., it makes a fresh copy of the underlying array and operates on the cloned array. Read more about CopyOnWriteArraySet here.

Syntax

boolean removeAll(Collection<?> c)

Argument

This method takes the collection object to be removed from the set as an argument.

Return value

This method returns true if the set changes due to the call (any one of the elements from the Collection is present and removed from the set). Otherwise, false will be returned.

Code

The code below demonstrates how the use of the removeAll() method:

import java.util.concurrent.CopyOnWriteArraySet;
import java.util.ArrayList;
class RemoveAll {
    public static void main( String args[] ) {
        // create a new queu which can have integer elements
        CopyOnWriteArraySet<Integer> set = new CopyOnWriteArraySet<>();
        // add elements to the set
        set.add(1);
        set.add(2);
        set.add(3);
        // create a new array list 
        ArrayList<Integer> list1 = new ArrayList<>();
        // add some elements to it 
        list1.add(1);
        list1.add(4);
        System.out.println("The CopyOnWriteArraySet is "+ set);
        System.out.println("The list1 is "+ list1);
        //remove all the elements of the list from the list
        System.out.println("\nCalling set.removeAll(list1). Is list changed - " + set.removeAll(list1));
        System.out.println("\nThe set is "+ set);
        
    }
}

Explanation

In the code above:

  • In line 1 and 2, we import the CopyOnWriteArraySet and ArrayList classes.

  • From line 6-10, we create a new CopyOnWriteArraySet object named set and add three elements (1,2,3) to the set object using the add() method.

  • From lines 12-15, we create a new ArrayList object named list1 and add two elements (1,4) to thelist1 object using the add() method.

  • In line 21, we use the removeAll() method to remove all the elements of list1 from set. The element 1 in the list1 is present in set. Hence, it is removed. The element 4 is not present in set, so it is not removed. After calling the removeAll() method, the content of the set object changes. true is returned. Now the set will be [2,3].

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