The correct answer is that a ClassCastException is thrown at runtime. This occurs because the Arrays.sort(Object[]) method internally casts each element to Comparable to compare and order them, and when the objects in the array do not implement the Comparable interface, that cast fails, triggering the exception. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of the natural ordering contract and the runtime behavior of sorting non-comparable objects—a common trap is assuming the code will compile but fail silently, when in fact the compiler allows it since the array type is Object, and the error only surfaces during execution. A reliable memory tip: if your objects lack a compareTo method, Arrays.sort will throw a fit—remember “No Comparable, no sorting, ClassCastException is the warning.”
1Z0-811 Arrays and Methods Practice Question
This 1Z0-811 practice question tests your understanding of arrays and methods. 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.
Which of the following correctly describes the effect of the method call 'Arrays.sort(myArray)' on an array of objects that do not implement Comparable?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A ClassCastException is thrown at runtime.
When `Arrays.sort(myArray)` is called on an array of objects that do not implement the `Comparable` interface, the method attempts to cast elements to `Comparable` to compare them. Since the objects do not implement `Comparable`, a `ClassCastException` is thrown at runtime. The `Arrays.sort(Object[])` method requires that all elements implement `Comparable`; otherwise, it cannot determine a natural ordering.
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 code does not compile because Arrays.sort requires a Comparator.
Why it's wrong here
Arrays.sort(Object[]) compiles; exception at runtime.
✓
A ClassCastException is thrown at runtime.
Why this is correct
Elements must implement Comparable.
Related concept
Read the scenario before looking for a memorised answer.
✗
The array is sorted using the natural order of the elements.
Why it's wrong here
Natural order requires Comparable implementation.
✗
The array is sorted using the order defined by the elements' equals method.
Why it's wrong here
Sorting uses compareTo, not equals.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the code will not compile (Option A) because they think `Comparable` is required at compile time, but the requirement is enforced at runtime via a cast, leading to a `ClassCastException`.
Detailed technical explanation
How to think about this question
Under the hood, `Arrays.sort(Object[])` delegates to `ComparableTimSort` or legacy `MergeSort`, which internally calls `((Comparable) a).compareTo(b)` on each element. If the element's class does not implement `Comparable`, the cast fails at runtime. A real-world scenario is sorting an array of custom `Person` objects without implementing `Comparable`; the developer must either implement `Comparable` or use the overloaded `Arrays.sort(T[], Comparator)` method.
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.
TExam Day Tips
→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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Arrays and Methods — This question tests Arrays and Methods — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: A ClassCastException is thrown at runtime. — When `Arrays.sort(myArray)` is called on an array of objects that do not implement the `Comparable` interface, the method attempts to cast elements to `Comparable` to compare them. Since the objects do not implement `Comparable`, a `ClassCastException` is thrown at runtime. The `Arrays.sort(Object[])` method requires that all elements implement `Comparable`; otherwise, it cannot determine a natural ordering.
What should I do if I get this 1Z0-811 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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