In Collection Framework, to make collection type object as unmodifiable java.Util.Collections class provides static methods to make these object as unmodifiable.

Collections Class Unmodifiable Methods

static Collection unmodifiableCollection(Collection<? extends T> c)	Returns an unmodifiable view of the specified collection.
static List unmodifiableList(List<? extends T> list)	Returns an unmodifiable view of the specified list.
static <K,V> Map<K,V> unmodifiableMap(Map<? extends K,? extends V> m)	Returns an unmodifiable view of the specified map.
static <K,V> NavigableMap<K,V> unmodifiableNavigableMap(NavigableMap<K,? extends V> m)	Returns an unmodifiable view of the given map.
static NavigableSet unmodifiableNavigableSet(NavigableSet s)	Returns an unmodifiable view of the given navigable set.
static Set unmodifiableSet(Set<? extends T> s)	Returns an unmodifiable view of the given set.
static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K,? extends V> m)	Returns an unmodifiable view of the given map.
static SortedSet unmodifiableSortedSet(SortedSet s)	Returns an unmodifiable view of the given  set.

Example: Synchronized Collections

In this example creating the blank type of collection and making it Unmodified. You can assign the same with collection objects.

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;

public class CollectionUnmodifiedExample {

	public static void main(String[] args) {
		Collection c = new ArrayList();
	    Collections.unmodifiableCollection(c);
	    Collections.unmodifiableList(new ArrayList());
	    Collections.unmodifiableMap(new HashMap());
	    Collections.unmodifiableSet(new HashSet());
	}

}

References

• https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html