HashSet retainAll() method in Java with Example
The retainAll() method of java.util.HashSet class is used to retain from this set all of its elements that are contained in the specified collection.
Syntax:
public boolean retainAll(Collection c)
Parameters: This method takes collection c as a parameter containing elements to be retained 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 retainAll() method.
Example 1:
import java.util.*;
public class GFG1 {
public static void main(String[] argv) throws Exception
{
try {
HashSet<Integer>
arrset1 = new HashSet<Integer>();
arrset1.add( 1 );
arrset1.add( 2 );
arrset1.add( 3 );
arrset1.add( 4 );
arrset1.add( 5 );
System.out.println( "HashSet before "
+ "retainAll() operation : "
+ arrset1);
HashSet<Integer>
arrset2 = new HashSet<Integer>();
arrset2.add( 1 );
arrset2.add( 2 );
arrset2.add( 3 );
System.out.println( "Collection Elements"
+ " to be retained : "
+ arrset2);
arrset1.retainAll(arrset2);
System.out.println( "HashSet after "
+ "retainAll() operation : "
+ arrset1);
}
catch (NullPointerException e) {
System.out.println( "Exception thrown : " + e);
}
}
}
|
Output:
HashSet before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
HashSet after retainAll() operation : [1, 2, 3]
Example 2: For NullPointerException
import java.util.*;
public class GFG1 {
public static void main(String[] argv) throws Exception
{
try {
HashSet<Integer>
arrset1 = new HashSet<Integer>();
arrset1.add( 1 );
arrset1.add( 2 );
arrset1.add( 3 );
arrset1.add( 4 );
arrset1.add( 5 );
System.out.println( "HashSet before "
+ "retainAll() operation : "
+ arrset1);
HashSet<Integer>
arrset2 = null ;
System.out.println( "Collection Elements"
+ " to be retained : "
+ arrset2);
System.out.println( "\nTrying to pass "
+ "null as a specified element\n" );
arrset1.retainAll(arrset2);
System.out.println( "HashSet after "
+ "retainAll() operation : "
+ arrset1);
}
catch (NullPointerException e) {
System.out.println( "Exception thrown : " + e);
}
}
}
|
Output:
HashSet before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : null
Trying to pass null as a specified element
Exception thrown : java.lang.NullPointerException
Last Updated :
24 Dec, 2018
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