This 1Z0-829 practice question tests your understanding of utilizing java object-oriented approach. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. A key principle to apply: double-checked locking. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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;
}
}Answer choices
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.
Option B is correct because 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.
Key principle: Double-checked locking
Common exam traps
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.
Detailed technical explanation
The double-checked locking pattern relies on the `volatile` keyword to establish a happens-before relationship, but without proper memory barriers, the JIT compiler or CPU can reorder the assignment of the instance variable before the constructor completes. This is a classic concurrency pitfall that was only fully resolved in Java 5 with the introduction of the Java Memory Model (JSR 133), which guarantees that `volatile` fields prevent reordering. In real-world scenarios, this bug can manifest as intermittent failures in multi-threaded environments, such as web servers or caching systems.
Key takeaway
Double-checked locking
Real-world example
A practitioner preparing for the 1Z0-829 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Double-checked locking Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Review double-checked locking, then practise related 1Z0-829 questions on the same topic to reinforce the concept.
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FAQ
Utilizing Java Object-Oriented Approach — This question tests Utilizing Java Object-Oriented Approach — Double-checked locking.
The correct answer is: It may still have a race condition due to instruction reordering. — Option B is correct because 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.
Review double-checked locking, then practise related 1Z0-829 questions on the same topic to reinforce the concept.
Double-checked locking
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Last reviewed: Jul 4, 2026
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