Set removeAll() method in Java with Examples

The removeAll() method of java.util.Set interface 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: This method throws NullPointerException if this set contains a null element and the specified collection does not permit null elements (optional), or if the specified collection is null.

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

Example 1:

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

import java.util.*;

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

        try {
            // Creating object of Set
            Set<Integer> set1 = new HashSet<Integer>();

            // Populating set1
            set1.add(1);
            set1.add(2);
            set1.add(3);
            set1.add(4);
            set1.add(5);

            // print set1
            System.out.println("Set before removeAll() operation : "
                               + set1);

            // Creating another object of Set
            Set<Integer> set2 = new HashSet<Integer>();
            set2.add(1);
            set2.add(2);
            set2.add(3);

            // print set2
            System.out.println("Collection Elements to be removed : "
                               + set2);

            // Removing elements from set
            // specified in set2
            // using removeAll() method
            set1.removeAll(set2);

            // print set1
            System.out.println("Set after removeAll() operation : "
                               + set1);
        }

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

Output:

Set before removeAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be removed : [1, 2, 3]
Set 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[] argv) throws Exception
    {
        try {

            // Creating object of Set
            Set<Integer> set1 = new HashSet<Integer>();

            // Populating set1
            set1.add(1);
            set1.add(2);
            set1.add(3);
            set1.add(4);
            set1.add(5);

            // print set1
            System.out.println("Set before removeAll() operation : "
                               + set1);

            // Creating another object of Set<Integer>
            Set<Integer> set2 = null;

            // print set2
            System.out.println("Collection Elements to be removed : "
                               + set2);

            System.out.println("\nTrying to pass "
                               + "null as a specified element\n");

            // Removing elements from set
            // specified in set2
            // using removeAll() method
            set1.removeAll(set2);

            // print set1
            System.out.println("Set after removeAll() operation : "
                               + set1);
        }

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

Output:

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

Trying to pass null as a specified element

Exception thrown : java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/Set.html#removeAll(java.util.Collection)