java.lang.UnsupportedOperationException – How to handle UnsupportedOperationException

Sotirios-Efstathios ManeasJuly 7th, 2014Last Updated: July 7th, 2014

0 1,056 4 minutes read

In this tutorial we will discuss about UnsupportedOperationException in Java. This exception is thrown to indicate that the requested operation is not supported.

This exception extends the RuntimeException class and thus, belongs to those exceptions that can be thrown during the operation of the Java Virtual Machine (JVM). It is an unchecked exception and thus, it does not need to be declared in a method’s or a constructor’s throws clause. Moreover, the UnsupportedOperationException exists since the 1.2 version of Java.

Finally, the UnsupportedOperationException is a member of the Java Collections Framework.

The Structure of UnsupportedOperationException

Constructors

UnsupportedOperationException()

Creates an instance of the UnsupportedOperationException class, setting null as its message.

UnsupportedOperationException(String s)

Creates an instance of the UnsupportedOperationException class, using the specified string as message. The string argument indicates the name of the class that threw the error.

UnsupportedOperationException(String message, Throwable cause)

Creates an instance of the UnsupportedOperationException class, using the specified parameters as message cause respectively.

UnsupportedOperationException(Throwable cause)

Creates an instance of the UnsupportedOperationException class, using the specified Throwable as cause. Also, the Throwable::toString() method specifies the message of the exception.

The UnsupportedOperationException in Java

The UnsupportedOperationException indicates that the requested operation cannot be performed, due to the fact that it is forbidden for that particular class. The following methods create unmodifiable views of different collections:

public static Collection unmodifiableCollection(Collection c)

Returns an unmodifiable view of the specified Collection.

public static Set unmodifiableSet(Set s)

Returns an unmodifiable view of the specified Set.

public static SortedSet unmodifiableSortedSet(SortedSet s)

Returns an unmodifiable view of the specified SortedSet.

public static List unmodifiableList(List list)

Returns an unmodifiable view of the specified List.

public static Map unmodifiableMap(Map m)

Returns an unmodifiable view of the specified Map.

public static SortedMap unmodifiableSortedMap(SortedMap m)

Returns an unmodifiable view of the specified SortedMap.

These views are read-only and thus, cannot be modified. If an application tries to modify such view, an UnsupportedOperationException is thrown. The following examples indicate the aforementioned cases:

UnsupportedOperationExceptionExample_Collection.java:

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Random;

public class UnsupportedOperationExceptionExampleCollection {
	private final static int TOTAL_ELEMS = 10;
	private final static Random random = new Random();
	
	public static void main(String[] args) {
		Collection integers = new HashSet(TOTAL_ELEMS);
		
		// Fill the collection with some random values.
		for(int i = 0; i < TOTAL_ELEMS; ++i)
			integers.add(random.nextInt());
		
		// Retrieve an unmodifiable view of the collection.
		Collection unmodifiableCollection = Collections.unmodifiableCollection(integers);
		
		// This statement throws an UnsupportedOperationException.
		unmodifiableCollection.add(random.nextInt());
	}
}

In this example, we created an instance of the HashSet class, which implements the Collection interface, and inserted a number of random values. Then, we retrieved an unmodifiable view of the Collection and tried to insert a new element, which resulted to an UnsupportedOperationException.

UnsupportedOperationExceptionExampleSet.java:

import java.util.Collections;
import java.util.HashSet;
import java.util.Random;
import java.util.Set;

public class UnsupportedOperationExceptionExampleSet {
	private final static int TOTAL_ELEMS = 10;
	private final static Random random = new Random();
	
	public static void main(String[] args) {
		Set integers = new HashSet(TOTAL_ELEMS);
		
		// Fill the set with some random values.
		for(int i = 0; i < TOTAL_ELEMS; ++i)
			integers.add(random.nextInt());
		
		// Retrieve an unmodifiable view of the set.
		Set unmodifiableSet = Collections.unmodifiableSet(integers);
		
		// This statement throws an UnsupportedOperationException.
		unmodifiableSet.add(random.nextInt());
	}
}

In this example, we created an instance of the HashSet class and inserted a number of random values. Then, we retrieved an unmodifiable view of the HashSet and tried to insert a new element, which resulted to an UnsupportedOperationException.

UnsupportedOperationExceptionExampleSortedSet.java:

import java.util.Collections;
import java.util.Random;
import java.util.SortedSet;
import java.util.TreeSet;

public class UnsupportedOperationExceptionExampleSortedSet {
	private final static int TOTAL_ELEMS = 10;
	private final static Random random = new Random();
	
	public static void main(String[] args) {
		TreeSet integers = new TreeSet();
		
		// Fill the tree set with some random values.
		for(int i = 0; i < TOTAL_ELEMS; ++i)
			integers.add(random.nextInt());
		
		// Retrieve an unmodifiable view of the tree set.
		SortedSet unmodifiableSortedSet = Collections.unmodifiableSortedSet(integers);
		
		// This statement throws an UnsupportedOperationException.
		unmodifiableSortedSet.add(random.nextInt());
	}
}

In this example, we created an instance of the TreeSet class and inserted a number of random values. Then, we retrieved an unmodifiable view of the TreeSet and tried to insert a new element, which resulted to an UnsupportedOperationException.

UnsupportedOperationExceptionExampleList.java:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class UnsupportedOperationExceptionExampleList {
	private final static int TOTAL_ELEMS = 10;
	private final static Random random = new Random();
	
	public static void main(String[] args) {
		List integers = new ArrayList(TOTAL_ELEMS);
		
		// Fill the list with some random values.
		for(int i = 0; i < TOTAL_ELEMS; ++i)
			integers.add(random.nextInt());
		
		// Retrieve an unmodifiable view of the list.
		List unmodifiableList = Collections.unmodifiableList(integers);
		
		// This statement throws an UnsupportedOperationException.
		unmodifiableList.add(random.nextInt());
	}
}

In this example, we created an instance of the ArrayList class and inserted a number of random values. Then, we retrieved an unmodifiable view of the ArrayList and tried to insert a new element, which resulted to an UnsupportedOperationException.

UnsupportedOperationExceptionExampleMap.java:

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

public class UnsupportedOperationExceptionExampleMap {
	private final static int TOTAL_ELEMS = 10;
	private final static Random random = new Random();
	
	public static void main(String[] args) {
		Map map = new HashMap();
		
		// Fill the map with some random values.
		for(int i = 0; i < TOTAL_ELEMS; ++i)
			map.put(("key_" + i), random.nextInt());
		
		// Retrieve an unmodifiable view of the map.
		Map unmodifiableMap = Collections.unmodifiableMap(map);
		
		// This statement throws an UnsupportedOperationException.
		unmodifiableMap.put("KEY", random.nextInt());
	}
}

In this example, we created an instance of the HashMap class and inserted a number of random values. Then, we retrieved an unmodifiable view of the HashMap and tried to insert a new element, which resulted to an UnsupportedOperationException.

UnsupportedOperationExceptionExampleSortedMap.java:

import java.util.Collections;
import java.util.Random;
import java.util.SortedMap;
import java.util.TreeMap;

public class UnsupportedOperationExceptionExampleSortedMap {
	private final static int TOTAL_ELEMS = 10;
	private final static Random random = new Random();
	
	public static void main(String[] args) {
		TreeMap map = new TreeMap();
		
		// Fill the tree map with some random values.
		for(int i = 0; i < TOTAL_ELEMS; ++i)
			map.put(("key_" + i), random.nextInt());
		
		// Retrieve an unmodifiable view of the tree map.
		SortedMap unmodifiableSortedMap = Collections.unmodifiableSortedMap(map);
		
		// This statement throws an UnsupportedOperationException.
		unmodifiableSortedMap.put("KEY", random.nextInt());
	}
}

In this example, we created an instance of the TreeMap class and inserted a number of random values. Then, we retrieved an unmodifiable view of the TreeMap and tried to insert a new element, which resulted to an UnsupportedOperationException.

How to deal with the UnsupportedOperationException

This exception is easy to deal with, because it indicates which method cannot be used. Thus, if your application requires the modification of some collection or data structures, you shall avoid using unmodifiable views.
Also, if this exception is thrown by a class of an external library, you shall consult its documentation, in order to understand why this particular exception is thrown.