Why do I get an UnsupportedOperationException when trying to remove an element from a List?

The java.lang.UnsupportedOperationException is thrown when an operation is not supported by a class. In the case of a List, this exception is typically thrown when you try to modify the list using one of the remove, add, or set methods, and the list is unmodifiable.

A list is considered unmodifiable when it cannot be modified, either because it is a fixed-size list, or because it is a view of another list that is not modifiable.

For example, the java.util.Arrays.asList() method returns a fixed-size list that is a view of an array. This list is unmodifiable, and any attempt to modify it will result in an UnsupportedOperationException.

Here is an example of how you can get an UnsupportedOperationException when trying to remove an element from a list:

import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("a", "b", "c");
        list.remove(1);  // This will throw an UnsupportedOperationException
    }
}

To fix this issue, you can create a new modifiable list from the unmodifiable list, using the java.util.ArrayList constructor.

For example:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> unmodifiableList = Arrays.asList("a", "b", "c");
        List<String> list = new ArrayList<>(unmodifiableList);
        list.remove(1);  // This will remove the element at index 1
    }
}

This will create a new modifiable ArrayList from the unmodifiable list, and allow you to remove elements from the list without getting an UnsupportedOperationException.