Arrays.asList() throws java.lang.UnsupportedOperationException

Arrays.asList() throws java.lang.UnsupportedOperationException

You might get the UnsupportedException when you tries to use the add() method in the List.

If your code looks something similar to this :

String[] data = new String[] {"hari","krushna"};
List<String> asList = Arrays.asList(data);
asList.add("test");

Then you will see the following exception :

java.lang.UnsupportedOperationException
at java.util.AbstractList.add(Unknown Source)
at java.util.AbstractList.add(Unknown Source)
at ArrayConvert.trial(ArrayConvert.java:14)
at ArrayConvert.main(ArrayConvert.java:8)

Solution of the above problem is :
 you need to create an ArrayList or LinkedList and add the objects to the newly created Array/LinkedList:

String[] data = new String[] {"","",""};
List<String> asList = Arrays.asList(data);
List<String> newList = new LinkedList<>(asList);
newList.add("test");

Reason for the UnsupportedOperationException:

Arrays.asList Method is returning a sub class object of Arrays class : java.util.Arrays.ArrayList

Following is the signature of the class :

private static class ArrayList<E> extends AbstractList<E> implements RandomAccess, java.io.Serializable

Here ArrayList extends java.util.AbstractList class.

Following are the add() method in AbstractList:

public boolean add(E e) {

 add(size(), e);

 return true;

}

public void add(int index, E element) {

  throw new UnsupportedOperationException();

}

As you see above add() method is not implemented, so when add() method is called directly from asList() object then it will throw an Exception.

This will be Runtime exception so difficult to identify at the time of coding.