AbstractCollection removeAll() method in Java with Example

The Java.util.AbstractCollection.removeAll(Collection col) method is used to remove all the elements from the AbstractCollection, present in the collection specified.

Syntax:

AbstractCollection.removeAll(Collection col)

Parameters: This method accepts a mandatory parameter col which is the collection whose elements are to be removed from the AbstractCollection.

Return Value: This method returns true if the AbstractCollection is altered due to the operation at all, else False.

Exception: The method throws NullPointerException if the specified collection is null.

Below programs illustrate the Java.util.AbstractCollection.removeAll(Collection col) method:

Program 1:

// Java code to illustrate removeAll()
import java.util.*;

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

        // Creating an empty AbstractCollection
        AbstractCollection<String> collection
            = new ArrayList<String>();

        // Use add() method to add
        // elements in the AbstractCollection
        collection.add("Geeks");
        collection.add("for");
        collection.add("Geeks");
        collection.add("10");
        collection.add("20");

        // Output the AbstractCollection
        System.out.println("AbstractCollection: "
                           + collection);

        // Creating an empty AbstractCollection
        AbstractCollection<String> colcollection
            = new ArrayList<String>();

        // Use add() method to add
        // elements in the AbstractCollection
        colcollection.add("Geeks");
        colcollection.add("for");
        colcollection.add("Geeks");

        // Remove the head using remove()
        boolean changed
            = collection.removeAll(colcollection);

        // Print the result
        if (changed)
            System.out.println("Collection removed");
        else
            System.out.println("Collection not removed");

        // Print the final AbstractCollection
        System.out.println("Final AbstractCollection: "
                           + collection);
    }
}

Output:

AbstractCollection: [Geeks, for, Geeks, 10, 20]
Collection removed
Final AbstractCollection: [10, 20]

Program 2:

// Java code to illustrate removeAll()
import java.util.*;

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

        // Creating an empty AbstractCollection
        AbstractCollection<Integer> collection
            = new ArrayList<Integer>();

        // Use add() method to
        // add elements in the AbstractCollection
        collection.add(1);
        collection.add(2);
        collection.add(3);
        collection.add(10);
        collection.add(20);

        // Output the AbstractCollection
        System.out.println("AbstractCollection: "
                           + collection);

        // Creating an empty AbstractCollection
        AbstractCollection<Integer> colcollection
            = new ArrayList<Integer>();

        // Use add() method to add elements
        // in the AbstractCollection
        colcollection.add(30);
        colcollection.add(40);
        colcollection.add(50);

        // Remove the head using remove()
        boolean changed
            = collection.removeAll(colcollection);

        // Print the result
        if (changed)
            System.out.println("Collection removed");
        else
            System.out.println("Collection not removed");

        // Print the final AbstractCollection
        System.out.println("Final AbstractCollection: "
                           + collection);
    }
}

Output:

AbstractCollection: [1, 2, 3, 10, 20]
Collection not removed
Final AbstractCollection: [1, 2, 3, 10, 20]