Oracle Java SE 21 Developer Professional 認定 1z0-830 試験問題:

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

2. Which of the following statements are correct?

A) None
B) You can use 'public' access modifier with all kinds of classes
C) You can use 'final' modifier with all kinds of classes
D) You can use 'protected' access modifier with all kinds of classes
E) You can use 'private' access modifier with all kinds of classes

3. Given:
java
Deque<Integer> deque = new ArrayDeque<>();
deque.offer(1);
deque.offer(2);
var i1 = deque.peek();
var i2 = deque.poll();
var i3 = deque.peek();
System.out.println(i1 + " " + i2 + " " + i3);
What is the output of the given code fragment?

A) 1 2 1
B) 2 1 2
C) 2 2 1
D) 1 1 1
E) 1 2 2
F) An exception is thrown.
G) 1 1 2
H) 2 1 1
I) 2 2 2

4. Which of the following isn't a valid option of the jdeps command?

A) --list-deps
B) --generate-module-info
C) --generate-open-module
D) --print-module-deps
E) --check-deps
F) --list-reduced-deps

5. Given:
java
Integer frenchRevolution = 1789;
Object o1 = new String("1789");
Object o2 = frenchRevolution;
frenchRevolution = null;
Object o3 = o2.toString();
System.out.println(o1.equals(o3));
What is printed?

A) true
B) Compilation fails.
C) A NullPointerException is thrown.
D) A ClassCastException is thrown.
E) false

質問と回答：