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Set removeAll() method in Java with Examples

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  • Last Updated : 30 Sep, 2019
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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)


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