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Oracle 1z1-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
Stream<String> strings = Stream.of("United", "States");
BinaryOperator<String> operator = (s1, s2) -> s1.concat(s2.toUpperCase()); String result = strings.reduce("-", operator); System.out.println(result); What is the output of this code fragment?

A) UnitedStates
B) United-States
C) -UnitedSTATES
D) -UNITEDSTATES
E) United-STATES
F) UNITED-STATES
G) -UnitedStates

2. Given:
java
interface SmartPhone {
boolean ring();
}
class Iphone15 implements SmartPhone {
boolean isRinging;
boolean ring() {
isRinging = !isRinging;
return isRinging;
}
}
Choose the right statement.

A) An exception is thrown at running Iphone15.ring();
B) Everything compiles
C) Iphone15 class does not compile
D) SmartPhone interface does not compile

3. Given:
java
var counter = 0;
do {
System.out.print(counter + " ");
} while (++counter < 3);
What is printed?

A) 1 2 3 4
B) An exception is thrown.
C) 0 1 2
D) 0 1 2 3
E) 1 2 3
F) Compilation fails.

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

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

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

A) 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.
B) The CopyOnWriteArrayList class does not allow null elements.
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 is not thread-safe and does not prevent interference amongconcurrent threads.
E) The CopyOnWriteArrayList class's iterator reflects all additions, removals, or changes to the list since the iterator was created.

Solutions: