SortedSet retainAll() method in Java with Examples

Last Updated : 21 Jan, 2021

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)

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