Why Am I Getting an UnsupportedOperationException When Using List.add()?

Java List.add() UnsupportedOperationException: Understanding and Resolving

Adding elements to a Java List should be straightforward, but sometimes an UnsupportedOperationException arises. Why does this happen?

In Java, not all List implementations support the add() method. A common culprit is the List returned by Arrays.asList(). As per its documentation, it's a "fixed-size" list that disallows structural modifications like adding elements.

Even if your List isn't the result of Arrays.asList(), other classes or libraries may provide Lists with limited mutability or that are immutable. To check if your List supports add(), consult its documentation or the JavaDocs for UnsupportedOperationException and List.add().

To resolve this issue, consider creating a copy of the unsupported List into a known-modifiable implementation like ArrayList:

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

This way, you can make modifications to the copied ArrayList without facing the UnsupportedOperationException.

The above is the detailed content of Why Am I Getting an UnsupportedOperationException When Using List.add()?. For more information, please follow other related articles on the PHP Chinese website!