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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

Question 1

Given:
java
Optional o1 = Optional.empty();
Optional o2 = Optional.of(1);
Optional o3 = Stream.of(o1, o2)
.filter(Optional::isPresent)
.findAny()
.flatMap(o -> o);
System.out.println(o3.orElse(2));
What is the given code fragment's output?

A. 0
B. An exception is thrown
C. Compilation fails
D. 1
E. Optional[1]
F. 2
G. Optional.empty

Question 2

Given:
java
var now = LocalDate.now();
var format1 = new DateTimeFormatter(ISO_WEEK_DATE);
var format2 = DateTimeFormatter.ISO_WEEK_DATE;
var format3 = new DateFormat(WEEK_OF_YEAR_FIELD);
var format4 = DateFormat.getDateInstance(WEEK_OF_YEAR_FIELD);
System.out.println(now.format(REPLACE_HERE));
Which variable prints 2025-W01-2 (present-day is 12/31/2024)?

A. format3
B. format2
C. format4
D. format1

Question 3

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

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

Question 4

Which of the followingisn'ta correct way to write a string to a file?

A. java
try (BufferedWriter writer = new BufferedWriter("file.txt")) {
writer.write("Hello");
}
B. java
try (FileWriter writer = new FileWriter("file.txt")) {
writer.write("Hello");
}
C. None of the suggestions
D. java
try (FileOutputStream outputStream = new FileOutputStream("file.txt")) { byte[] strBytes = "Hello".getBytes(); outputStream.write(strBytes);
}
E. java
try (PrintWriter printWriter = new PrintWriter("file.txt")) {
printWriter.printf("Hello %s", "James");
}
F. java
Path path = Paths.get("file.txt");
byte[] strBytes = "Hello".getBytes();
Files.write(path, strBytes);

Question 5

Given:
java
StringBuffer us = new StringBuffer("US");
StringBuffer uk = new StringBuffer("UK");
Stream<StringBuffer> stream = Stream.of(us, uk);
String output = stream.collect(Collectors.joining("-", "=", ""));
System.out.println(output);
What is the given code fragment's output?

A. -US=UK
B. =US-UK
C. US=UK
D. US-UK
E. An exception is thrown.
F. Compilation fails.

Solutions: