AbstractSet removeAll() Method in Java with Examples

The removeAll() method of Java AbstractSet class is used to remove from this set all of its elements that are contained in the specified collection.

Syntax:

public boolean removeAll(Collection c)

Parameters: This method takes collection c as a parameter containing elements to be removed from this set.

Returns Value: This method returns true if this set changed as a result of the call.

Exception: The method throws three types of exception:

• UnsupportedOperationException – This is thrown if the operation is not supported by this set.
• ClassCastException – This is thrown when the class of an element of this set is not compatible with the specified collection.
• NullPointerException – This is thrown when this set contains a null element and the specified collection does not permit null elements, or if the collection is null.

Below are the examples to illustrate the removeAll() method.

Program 1:

// Java program to demonstrate
// removeAll() method for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] args) throws Exception
    {

        try {

            // Creating object of AbstractSet<Integer>
            AbstractSet<Integer>
                abs_set = new TreeSet<Integer>();

            // Populating abs_set
            abs_set.add(1);
            abs_set.add(2);
            abs_set.add(3);
            abs_set.add(4);
            abs_set.add(5);

            // print abs_set
            System.out.println("AbstractSet before "
                               + "removeAll() operation : "
                               + abs_set);

            // Creating another object of ArrayList<Integer>
            Collection<Integer>
                arrlist2 = new ArrayList<Integer>();
            arrlist2.add(1);
            arrlist2.add(2);
            arrlist2.add(3);

            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrlist2);

            // Removing elements from AbstractSet
            // specified in arrlist2
            // using removeAll() method
            abs_set.removeAll(arrlist2);

            // print arrlist1
            System.out.println("AbstractSet after "
                               + "removeAll() operation : "
                               + abs_set);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

AbstractSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : [1, 2, 3]
AbstractSet after removeAll() operation : [4, 5]

Example 2: For NullPointerException

// Java program to demonstrate
// removeAll() method for Integer value

import java.util.*;

public class GFG1 {
    public static void main(String[] args) throws Exception
    {

        try {

            // Creating object of AbstractSet<Integer>
            AbstractSet<Integer>
                abs_set = new TreeSet<Integer>();

            // Populating abs_set
            abs_set.add(1);
            abs_set.add(2);
            abs_set.add(3);
            abs_set.add(4);
            abs_set.add(5);

            // print abs_set
            System.out.println("AbstractSet before "
                               + "removeAll() operation : "
                               + abs_set);

            // Creating another object of ArrayList<Integer>
            Collection<Integer>
                arrlist2 = new ArrayList<Integer>();
            arrlist2 = null;

            // print arrlist2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrlist2);

            // Removing elements from AbstractSet
            // specified in arrlist2
            // using removeAll() method
            abs_set.removeAll(arrlist2);

            // print arrlist1
            System.out.println("AbstractSet after "
                               + "removeAll() operation : "
                               + abs_set);
        }

        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

AbstractSet before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : null
Exception thrown : java.lang.NullPointerException