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The removeAll() method in CopyOnWriteArrayList class that removes all the elements that are contained in the specified collection from the CopyOnArrayList object you call on. Syntax:

public boolean removeAll(Collection collection)

Parameter: The method accepts only a single parameter collection which is to be removed from the calling object. Return Value: This method returns a boolean value. It returns true if this remove operation is successful. Exception: This method throws following exceptions:

ClassCastException: if the class of an element of this list is incompatible with the specified collection.
NullPointerException: if the specified collection is null or if this list contains a null element and the specified collection does not permit null elements.

Below examples illustrates the removeAll() method: Example 1:

Java

// Java program to demonstrate removeAll() method

import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArrayList;

public class Demo {

    public static void main(String args[])
    {

        // Get the CopyOnWriteArrayList
        CopyOnWriteArrayList<String> wishlist
            = new CopyOnWriteArrayList<>();

        // Add the elements in the CopyOnWriteArrayList
        wishlist.add("TV");
        wishlist.add("computer");
        wishlist.add("play station");
        wishlist.add("mobile");
        wishlist.add("smart watch");

        // Print the CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: \n"
                           + wishlist);

        // Get the collection to be removed
        ArrayList<String> checkList
            = new ArrayList<>();

        checkList.add("play station");
        checkList.add("TV");
        checkList.add("mobile");

        System.out.println("\nCollection to be removed:\n"
                           + checkList);

        // Remove the collection from CopyOnWriteArrayList
        // using removeAll() method
        wishlist.removeAll(checkList);

        // Print the CopyOnWriteArrayList after removal
        System.out.println("\nAfter removal of collection"
                           + " from CopyOnWriteArrayList:\n"
                           + wishlist);
    }
}

Output:

CopyOnWriteArrayList: 
[TV, computer, play station, mobile, smart watch]

Collection to be removed:
[play station, TV, mobile]

After removal of collection from CopyOnWriteArrayList:
[computer, smart watch]

Example 2: To show NullPointerException

Java

// Java program to demonstrate removeAll() method

import java.util.ArrayList;
import java.util.concurrent.CopyOnWriteArrayList;

public class Demo {

    public static void main(String args[])
    {

        // Get the CopyOnWriteArrayList
        CopyOnWriteArrayList<String> wishlist
            = new CopyOnWriteArrayList<>();

        // Add the elements in the CopyOnWriteArrayList
        wishlist.add("TV");
        wishlist.add("computer");
        wishlist.add("play station");
        wishlist.add("mobile");
        wishlist.add("smart watch");

        // Print the CopyOnWriteArrayList
        System.out.println("CopyOnWriteArrayList: \n"
                           + wishlist);

        // Get the collection to be removed
        ArrayList<String> checkList
            = null;
        System.out.println("\nCollection to be removed: "
                           + checkList);

        try {

            // Remove the collection from CopyOnWriteArrayList
            // using removeAll() method
            wishlist.removeAll(checkList);
        }
        catch (Exception e) {

            // Print the Exception
            System.out.println("\nException thrown"
                               + " while removing null "
                               + "from the CopyOnWriteArrayList: \n"
                               + e);
        }
    }
}

Output:

CopyOnWriteArrayList: 
[TV, computer, play station, mobile, smart watch]

Collection to be removed: null

Exception thrown while removing null from the CopyOnWriteArrayList: 
java.lang.NullPointerException

CopyOnWriteArrayList removeAll() method in Java with Examples

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