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HashSet removeAll() method in Java with Example

  • Last Updated : 24 Dec, 2018

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:

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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 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);
        }
    }
}
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




// 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);
        }
    }
}
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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