Utilizing Java Object-Oriented Approach →hardMultiple ChoiceObjective-mapped

1Z0-829 Double-checked locking Practice Question

Exhibit

public class Singleton {
    private static volatile Singleton instance;
    private Singleton() {}
    public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}

Refer to the exhibit. Which statement about this Singleton implementation is correct?

⚠ Common exam trap

Oracle often tests the misconception that volatile is unnecessary in double-checked locking. Without volatile, instruction reordering can expose a partially constructed object, even with synchronized blocks.

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

It may still have a race condition due to instruction reordering.

The provided Singleton implementation uses double-checked locking without declaring the instance variable as volatile. Without volatile, the JVM may reorder instructions such that a thread reads a non-null reference to a partially constructed object, leading to a race condition. This is a classic pitfall in Java concurrency.

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1Z0-829 Double-checked locking Practice Question

Exhibit

Why each option matters

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