SortedSet retainAll() method in Java with Examples

The retainAll() method of SortedSet interface is used to retain from this SortedSet, 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 SortedSet.

Return Value: This method returns true if this SortedSet 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.

Note: The retainAll() method in SortedSet is inherited from the Set interface in Java.

Below are the examples to illustrate the retainAll() method.

Example 1:

Java

// Java program to demonstrate
// retainAll() method for Sorted set

import java.util.*;

public class GFG1 {
    public static void main(String[] args)
        throws Exception
    {

        try {

            // Creating object of Set
            SortedSet<Integer> arrset1
                = new TreeSet<Integer>();

            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);

            // print arrset1
            System.out.println(
                "Set before "
                + "retainAll() operation : "
                + arrset1);

            // Creating another object of  Set
            SortedSet<Integer> arrset2
                = new TreeSet<Integer>();
            arrset2.add(1);
            arrset2.add(2);
            arrset2.add(3);

            // print arrset2
            System.out.println(
                "Collection Elements"
                + " to be retained : "
                + arrset2);

            // Removing elements from arrset
            // specified in arrset2
            // using retainAll() method
            arrset1.retainAll(arrset2);

            // print arrset1
            System.out.println(
                "Set after "
                + "retainAll() operation : "
                + arrset1);
        }

        catch (NullPointerException e) {
            System.out.println(e);
        }
    }
}

Output:

Set before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : [1, 2, 3]
Set after retainAll() operation : [1, 2, 3]

Example 2: For NullPointerException.

Java

// Java program to demonstrate
// retainAll() method for Sorted set

import java.util.*;

public class GFG1 {
    public static void main(String[] args)
        throws Exception
    {
        try {

            // Creating object of SortedSet<Integer>
            SortedSet<Integer> arrset1
                = new TreeSet<Integer>();

            // Populating arrset1
            arrset1.add(1);
            arrset1.add(2);
            arrset1.add(3);
            arrset1.add(4);
            arrset1.add(5);

            // print arrset1
            System.out.println(
                "Set before "
                + "retainAll() operation : "
                + arrset1);

            // Creating another object of Set<Integer>
            SortedSet<Integer> arrset2 = null;

            // print arrset2
            System.out.println(
                "Collection Elements "
                + "to be retained : "
                + arrset2);

            System.out.println(
                "\nTrying to pass "
                + "null as a "
                + "specified element\n");

            // Removing elements from arrset
            // specified in arrset2
            // using retainAll() method
            arrset1.retainAll(arrset2);

            // print arrset1
            System.out.println(
                "Set after "
                + "retainAll() operation : "
                + arrset1);
        }

        catch (NullPointerException e) {
            System.out.println(e);
        }
    }
}

Output:

Set before retainAll() operation : [1, 2, 3, 4, 5]
Collection Elements to be retained : null

Trying to pass null as a specified element

java.lang.NullPointerException

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/Set.html#retainAll(java.util.Collection)