1Z0-829 Working with Streams and Lambda Expressions Practice Question
Which TWO are valid ways to obtain a Stream from a List<String> named 'list'? (Choose two.)
⚠ Common exam trap
Test-takers frequently confuse `Stream.of(list)` with `list.stream()`, not realizing that `Stream.of()` treats the collection as a single element, and may also incorrectly think `Stream` can be instantiated with `new` like a regular class.
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
✓
list.stream()
Options A and E are correct. The `List` interface provides the `stream()` method to obtain a sequential stream and `parallelStream()` to obtain a parallel stream. Option B is incorrect because `Stream.of(list)` treats the list itself as a single element, producing a `Stream<List<String>>` rather than a `Stream<String>`. Option C is incorrect because `Arrays.stream(list.toArray())` would work if you had a String array, but it returns a `Stream<Object>` since `toArray()` returns `Object[]`; this is not type-safe and not a direct way to get a stream from a list. Option D is incorrect because `Stream` is an interface and cannot be instantiated with `new`.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
list.stream()
Why this is correct
Correct. The List interface provides the stream() method to obtain a sequential Stream<String>.
- ✗
Stream.of(list)
Why it's wrong here
Incorrect. Stream.of(list) treats the list itself as a single element, producing a Stream<List<String>>, not Stream<String>.
- ✗
Arrays.stream(list.toArray())
Why it's wrong here
Incorrect. Arrays.stream(list.toArray()) returns a Stream<Object> because toArray() returns Object[], not a Stream<String>. It is not a direct or type-safe way to obtain a stream from a List.
- ✗
new Stream<>(list)
Why it's wrong here
Incorrect. Stream is an interface and cannot be instantiated with the new keyword.
- ✓
list.parallelStream()
Why this is correct
Correct. The List interface provides the parallelStream() method to obtain a parallel Stream<String>.
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