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Oracle 1z1-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Given:
java
try (FileOutputStream fos = new FileOutputStream("t.tmp");
ObjectOutputStream oos = new ObjectOutputStream(fos)) {
fos.write("Today");
fos.writeObject("Today");
oos.write("Today");
oos.writeObject("Today");
} catch (Exception ex) {
// handle exception
}
Which statement compiles?

A) oos.writeObject("Today");
B) fos.write("Today");
C) oos.write("Today");
D) fos.writeObject("Today");

2. Given:
java
import java.io.*;
class A implements Serializable {
int number = 1;
}
class B implements Serializable {
int number = 2;
}
public class Test {
public static void main(String[] args) throws Exception {
File file = new File("o.ser");
A a = new A();
var oos = new ObjectOutputStream(new FileOutputStream(file));
oos.writeObject(a);
oos.close();
var ois = new ObjectInputStream(new FileInputStream(file));
B b = (B) ois.readObject();
ois.close();
System.out.println(b.number);
}
}
What is the given program's output?

A) 1
B) Compilation fails
C) 2
D) NotSerializableException
E) ClassCastException

3. You are working on a module named perfumery.shop that depends on another module named perfumery.
provider.
The perfumery.shop module should also make its package perfumery.shop.eaudeparfum available to other modules.
Which of the following is the correct file to declare the perfumery.shop module?

A) File name: module-info.perfumery.shop.java
java
module perfumery.shop {
requires perfumery.provider;
exports perfumery.shop.eaudeparfum.*;
}
B) File name: module.java
java
module shop.perfumery {
requires perfumery.provider;
exports perfumery.shop.eaudeparfum;
}
C) File name: module-info.java
java
module perfumery.shop {
requires perfumery.provider;
exports perfumery.shop.eaudeparfum;
}

4. Given:
java
public class Test {
static int count;
synchronized Test() {
count++;
}
public static void main(String[] args) throws InterruptedException {
Runnable task = Test::new;
Thread t1 = new Thread(task);
Thread t2 = new Thread(task);
t1.start();
t2.start();
t1.join();
t2.join();
System.out.println(count);
}
}
What is the given program's output?

A) It's either 0 or 1
B) It's either 1 or 2
C) It's always 2
D) It's always 1
E) Compilation fails

5. Given:
java
public class Test {
public static void main(String[] args) throws IOException {
Path p1 = Path.of("f1.txt");
Path p2 = Path.of("f2.txt");
Files.move(p1, p2);
Files.delete(p1);
}
}
In which case does the given program throw an exception?

A) File f1.txt exists while file f2.txt doesn't
B) File f2.txt exists while file f1.txt doesn't
C) An exception is always thrown
D) Both files f1.txt and f2.txt exist
E) Neither files f1.txt nor f2.txt exist

Solutions: