Oracle 1z0-830 real exam prep : Java SE 21 Developer Professional

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Oracle 1z0-830 Exam Syllabus Topics:

Oracle Java SE 21 Developer Professional Sample Questions:

1. Which of the following suggestions compile?(Choose two.)

A) java
sealed class Figure permits Rectangle {}
final class Rectangle extends Figure {
float length, width;
}
B) java
sealed class Figure permits Rectangle {}
public class Rectangle extends Figure {
float length, width;
}
C) java
public sealed class Figure
permits Circle, Rectangle {}
final sealed class Circle extends Figure {
float radius;
}
non-sealed class Rectangle extends Figure {
float length, width;
}
D) java
public sealed class Figure
permits Circle, Rectangle {}
final class Circle extends Figure {
float radius;
}
non-sealed class Rectangle extends Figure {
float length, width;
}

2. What does the following code print?
java
import java.util.stream.Stream;
public class StreamReduce {
public static void main(String[] args) {
Stream<String> stream = Stream.of("J", "a", "v", "a");
System.out.print(stream.reduce(String::concat));
}
}

A) Compilation fails
B) null
C) Optional[Java]
D) Java

3. Given:
java
Runnable task1 = () -> System.out.println("Executing Task-1");
Callable<String> task2 = () -> {
System.out.println("Executing Task-2");
return "Task-2 Finish.";
};
ExecutorService execService = Executors.newCachedThreadPool();
// INSERT CODE HERE
execService.awaitTermination(3, TimeUnit.SECONDS);
execService.shutdownNow();
Which of the following statements, inserted in the code above, printsboth:
"Executing Task-2" and "Executing Task-1"?

A) execService.call(task2);
B) execService.execute(task1);
C) execService.call(task1);
D) execService.execute(task2);
E) execService.run(task1);
F) execService.submit(task2);
G) execService.run(task2);
H) execService.submit(task1);

4. 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 compiles.
C) It throws an exception at runtime.

5. Which three of the following are correct about the Java module system?

A) We must add a module descriptor to make an application developed using a Java version prior to SE9 run on Java 11.
B) The unnamed module exports all of its packages.
C) The unnamed module can only access packages defined in the unnamed module.
D) Code in an explicitly named module can access types in the unnamed module.
E) If a request is made to load a type whose package is not defined in any known module, then the module system will attempt to load it from the classpath.
F) If a package is defined in both a named module and the unnamed module, then the package in the unnamed module is ignored.

Solutions: