The retainAll() method of java.util.LinkedHashSet 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:
// Java program to demonstrate// retainAll() method for Integer value import java.util.*; public class GFG1 { public static void main(String[] argv) throws Exception { try { // Creating object of LinkedHashSet<Integer> LinkedHashSet<Integer> set1 = new LinkedHashSet<Integer>(); // Populating set1 set1.add(1); set1.add(2); set1.add(3); set1.add(4); set1.add(5); // print set1 System.out.println("LinkedHashSet before " + "retainAll() operation : " + set1); // Creating another object of LinkedHashSet<Integer> LinkedHashSet<Integer> set2 = new LinkedHashSet<Integer>(); set2.add(1); set2.add(2); set2.add(3); // print set2 System.out.println("Collection Elements" + " to be retained : " + set2); // Removing elements from set // specified in set2 // using retainAll() method set1.retainAll(set2); // print set1 System.out.println("LinkedHashSet after " + "retainAll() operation : " + set1); } catch (NullPointerException e) { System.out.println("Exception thrown : " + e); } }} |
Output:
LinkedHashSet before retainAll() operation : [1, 2, 3, 4, 5] Collection Elements to be retained : [1, 2, 3] LinkedHashSet after retainAll() operation : [1, 2, 3]
Example 2: For NullPointerException
// Java program to demonstrate// retainAll() method for Integer value import java.util.*; public class GFG1 { public static void main(String[] argv) throws Exception { try { // Creating object of LinkedHashSet<Integer> LinkedHashSet<Integer> set1 = new LinkedHashSet<Integer>(); // Populating set1 set1.add(1); set1.add(2); set1.add(3); set1.add(4); set1.add(5); // print set1 System.out.println("LinkedHashSet before " + "retainAll() operation : " + set1); // Creating another object of LinkedHashSet<Integer> LinkedHashSet<Integer> set2 = null; // print set2 System.out.println("Collection Elements" + " to be retained : " + set2); System.out.println("\nTrying to pass " + "null as a specified element\n"); // Removing elements from set // specified in set2 // using retainAll() method set1.retainAll(set2); // print set1 System.out.println("LinkedHashSet after " + "retainAll() operation : " + set1); } catch (NullPointerException e) { System.out.println("Exception thrown : " + e); } }} |
Output:
LinkedHashSet 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
