Collections unmodifiableSet() method in Java with Examples

The unmodifiableSet() method of java.util.Collections class is used to return an unmodifiable view of the specified set. This method allows modules to provide users with “read-only” access to internal sets. Query operations on the returned set “read through” to the specified set, and attempts to modify the returned set, whether direct or via its iterator, result in an UnsupportedOperationException.

The returned set will be serializable if the specified set is serializable.

Syntax:

public static <T> Set<T> unmodifiableSet(Set<? extends T> s)

Parameters: This method takes the set as a parameter for which an unmodifiable view is to be returned.

Return Value: This method returns an unmodifiable view of the specified set.

Below are the examples to illustrate the unmodifiableSet() method

Example 1:

// Java program to demonstrate
// unmodifiableSet() method
// for <Character> value

import java.util.*;

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

        try {

            // creating object of HashSet<Character>
            Set<Character> set = new HashSet<Character>();

            // populate the table
            set.add('X');
            set.add('Y');

            // make the set unmodifiable
            Set<Character>
                immutableSet = Collections
                                   .unmodifiableSet(set);

            // printing unmodifiableSet
            System.out.println("unmodifiable Set: "
                               + immutableSet);
        }

        catch (UnsupportedOperationException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

unmodifiable Set: [X, Y]

Example 2: For UnsupportedOperationException

// Java program to demonstrate
// unmodifiableSet() method
// for <Character> value

import java.util.*;

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

        try {

            // creating object of HashSet<Character>
            Set<Character> set = new HashSet<Character>();

            // populate the table
            set.add('X');
            set.add('Y');

            // make the set unmodifiable
            Set<Character>
                immutableSet = Collections
                                   .unmodifiableSet(set);

            // printing unmodifiableSet
            System.out.println("unmodifiable Set: "
                               + immutableSet);

            System.out.println("\nTrying to modify"
                               + " the unmodifiable set");
            immutableSet.add('Z');
        }

        catch (UnsupportedOperationException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output:

unmodifiable Set: [X, Y]

Trying to modify the unmodifiable set
Exception thrown : java.lang.UnsupportedOperationException