The answer is that this singleton implementation is not thread-safe because two threads could simultaneously create different instances. The core issue lies in the lack of atomicity between the null-check (`if (instance == null)`) and the instantiation (`instance = new Singleton()`). In a multithreaded environment, both threads can evaluate the condition as true before either has completed the assignment, resulting in two distinct objects and breaking the singleton guarantee. On the Oracle Java Foundations 1Z0-811 exam, this scenario tests your understanding of concurrency hazards and the need for synchronization or a static initializer. A common trap is assuming a simple null-check is sufficient; the exam expects you to recognize that the check-and-create sequence must be atomic. Memory tip: think of it as a race to the constructor — without a lock, two runners can both see an empty finish line.
1Z0-811 Object-Oriented Programming Practice Question
This 1Z0-811 practice question tests your understanding of object-oriented programming. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. 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.
Exhibit
public class Singleton { private static Singleton instance; private Singleton() {} public static Singleton getInstance() { if (instance == null) { instance = new Singleton(); } return instance; } }
Refer to the exhibit. What is the potential issue with this singleton implementation in a multithreaded environment?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Not thread-safe; two threads could simultaneously create different instances
The if-check and instantiation are not atomic. Two threads could both see instance == null and create separate instances, violating the singleton guarantee.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The getInstance() method should be non-static
Why it's wrong here
A static method is appropriate for a singleton to provide global access without an instance.
✗
Compilation error because the constructor is private
Why it's wrong here
Private constructor is intended and does not cause a compile error.
✗
Memory leak because instances are never garbage collected
Why it's wrong here
The singleton holds a reference, so it is not garbage collected, but this is not a leak; it's intentional.
✓
Not thread-safe; two threads could simultaneously create different instances
Why this is correct
Correct. The check-then-act sequence is not synchronized.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 1Z0-811 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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which 1Z0-811 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Object-Oriented Programming — This question tests Object-Oriented Programming — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Not thread-safe; two threads could simultaneously create different instances — The if-check and instantiation are not atomic. Two threads could both see instance == null and create separate instances, violating the singleton guarantee.
What should I do if I get this 1Z0-811 question wrong?
Identify which 1Z0-811 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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