Question 316 of 513
1Z0-829 Working with Arrays and Collections Practice Question
Exhibit
Refer to the exhibit.
```java
import java.util.*;
import java.util.stream.*;
public class Test {
public static void main(String[] args) {
List<String> list = List.of("a", "b", "c");
var result = list.stream()
.filter(s -> s.startsWith("b"))
.collect(Collectors.toUnmodifiableList());
result.add("d");
System.out.println(result);
}
}
```What is the result of executing this code?
⚠ Common exam trap
The trap is that candidates may not know that `Collectors.toUnmodifiableList()` returns an immutable list. They might think they can add elements to it, expecting the output to be something like `[b, d]`, but instead an `UnsupportedOperationException` is thrown at runtime.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Runtime exception
The code uses `Collectors.toUnmodifiableList()` which returns an unmodifiable list. Attempting to add an element to this list throws an `UnsupportedOperationException` at runtime. Therefore, option C (Runtime exception) is correct.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Compilation error
Why it's wrong here
The code compiles successfully; all APIs are valid.
- ✗
[b]
Why it's wrong here
If the add were allowed, it would print [b], but it throws an exception.
- ✓
Runtime exception
Why this is correct
Collectors.toUnmodifiableList returns an immutable list, calling add throws UnsupportedOperationException.
- ✗
[b, d]
Why it's wrong here
The list is immutable, so add fails.
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Last reviewed: Jul 4, 2026
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