Why Am I Getting an UnsupportedOperationException When Adding to a Java List?

UnsupportedOperationException When Adding to Java List

When attempting to add objects to a List, you may encounter an UnsupportedOperationException. This exception signifies that the specific list implementation being used does not support adding new elements.

One common scenario where this error can occur is when working with a list returned by the Arrays.asList() method. This method specifically creates a fixed-size list that prohibits any structural modifications, such as adding or removing elements.

To determine if a list implementation supports adding, consult the documentation for the List.add() method. It explicitly states that adding is an "(optional operation)". This means that different list implementations may handle adding differently.

As a potential workaround, consider creating a copy of the list into a modifiable implementation, such as ArrayList:

<code class="java">seeAlso = new ArrayList<>(seeAlso);</code>

By using a modifiable implementation, you can ensure that adding new elements to the list is supported.

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