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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("A");
list.add("B");
list.add("C");
// Writing in one thread
new Thread(() -> {
list.add("D");
System.out.println("Element added: D");
}).start();
// Reading in another thread
new Thread(() -> {
for (String element : list) {
System.out.println("Read element: " + element);
}
}).start();
What is printed?

A) It throws an exception.
B) It prints all elements, but changes made during iteration may not be visible.
C) It prints all elements, including changes made during iteration.
D) Compilation fails.

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

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

3. Which of the following java.io.Console methods doesnotexist?

A) read()
B) readPassword(String fmt, Object... args)
C) reader()
D) readLine(String fmt, Object... args)
E) readLine()
F) readPassword()

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

5. Given:
java
List<String> abc = List.of("a", "b", "c");
abc.stream()
.forEach(x -> {
x = x.toUpperCase();
});
abc.stream()
.forEach(System.out::print);
What is the output?

A) abc
B) ABC
C) An exception is thrown.
D) Compilation fails.

Solutions: