HashSet removeAll() method in Java with Example

The removeAll() method of java.util.HashSet 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: 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:

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// 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 HashSet<Integer>
            HashSet<Integer>
                arrset1 = new HashSet<Integer>();
  
            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);
  
            // print arrset1
            System.out.println("HashSet before "
                               + "removeAll() operation : "
                               + arrset1);
  
            // Creating another object of  HashSet<Integer>
            HashSet<Integer>
                arrset2 = new HashSet<Integer>();
            arrset2.add(1);
            arrset2.add(2);
            arrset2.add(3);
  
            // print arrset2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrset2);
  
            // Removing elemnts from arrset
            // specified in arrset2
            // using removeAll() method
            arrset1.removeAll(arrset2);
  
            // print arrset1
            System.out.println("HashSet after "
                               + "removeAll() operation : "
                               + arrset1);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

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Output:

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

Example 2: For NullPointerException

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// 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 HashSet<Integer>
            HashSet<Integer>
                arrset1 = new HashSet<Integer>();
  
            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);
  
            // print arrset1
            System.out.println("HashSet before "
                               + "removeAll() operation : "
                               + arrset1);
  
            // Creating another object of  HashSet<Integer>
            HashSet<Integer>
                arrset2 = null;
  
            // print arrset2
            System.out.println("Collection Elements"
                               + " to be removed : "
                               + arrset2);
  
            System.out.println("\nTrying to pass "
                               + "null as a specified element\n");
  
            // Removing elemnts from arrset
            // specified in arrset2
            // using removeAll() method
            arrset1.removeAll(arrset2);
  
            // print arrset1
            System.out.println("HashSet after "
                               + "removeAll() operation : "
                               + arrset1);
        }
  
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

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Output:

HashSet 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


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