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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
Object input = 42;
String result = switch (input) {
case String s -> "It's a string with value: " + s;
case Double d -> "It's a double with value: " + d;
case Integer i -> "It's an integer with value: " + i;
};
System.out.println(result);
What is printed?

A) null
B) It's a string with value: 42
C) It's an integer with value: 42
D) It's a double with value: 42
E) It throws an exception at runtime.
F) Compilation fails.

2. Given:
java
Deque<Integer> deque = new ArrayDeque<>();
deque.offer(1);
deque.offer(2);
var i1 = deque.peek();
var i2 = deque.poll();
var i3 = deque.peek();
System.out.println(i1 + " " + i2 + " " + i3);
What is the output of the given code fragment?

A) 1 2 1
B) 1 1 2
C) 2 1 2
D) 1 2 2
E) An exception is thrown.
F) 1 1 1
G) 2 1 1
H) 2 2 2
I) 2 2 1

3. Given:
java
List<Long> cannesFestivalfeatureFilms = LongStream.range(1, 1945)
.boxed()
.toList();
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
cannesFestivalfeatureFilms.stream()
.limit(25)
.forEach(film -> executor.submit(() -> {
System.out.println(film);
}));
}
What is printed?

A) Numbers from 1 to 25 randomly
B) Compilation fails
C) Numbers from 1 to 1945 randomly
D) Numbers from 1 to 25 sequentially
E) An exception is thrown at runtime

4. Given:
java
var sList = new CopyOnWriteArrayList<Customer>();
Which of the following statements is correct?

A) The CopyOnWriteArrayList class is not thread-safe and does not prevent interference amongconcurrent threads.
B) The CopyOnWriteArrayList class does not allow null elements.
C) The CopyOnWriteArrayList class is a thread-safe variant of ArrayList where all mutative operations are implemented by making a fresh copy of the underlying array.
D) The CopyOnWriteArrayList class's iterator reflects all additions, removals, or changes to the list since the iterator was created.
E) Element-changing operations on iterators of CopyOnWriteArrayList, such as remove, set, and add, are supported and do not throw UnsupportedOperationException.

5. Given:
java
public class ThisCalls {
public ThisCalls() {
this(true);
}
public ThisCalls(boolean flag) {
this();
}
}
Which statement is correct?

A) It does not compile.
B) It throws an exception at runtime.
C) It compiles.

Solutions: