Quick Answer
The answer is an ArrayIndexOutOfBoundsException. This occurs because the method attempts to access arr[1] without first verifying that the array length is at least 2, and since Java arrays are zero-indexed, an array of length 1 only has a valid index of 0. The JVM performs runtime bounds checking, so accessing arr[1] on a single-element array immediately throws the exception. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of array bounds and the importance of defensive programming—a common trap is assuming the method will work with any array, but it fails silently only in logic, not syntax. Remember the memory tip: “Check the length before you index the strength”—always validate array size when accessing multiple indices to avoid runtime crashes.
This 1Z0-811 practice question tests your understanding of arrays and methods. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
Given the method: 'public static void swapFirstTwo(int[] arr) { int temp = arr[0]; arr[0] = arr[1]; arr[1] = temp; }'. What is the effect of calling this method with an array of length 1?
An ArrayIndexOutOfBoundsException is thrown.
Index 1 is out of bounds for length 1.
The first element is swapped with itself.
Why wrong: No swap occurs due to exception.
A new array with length 2 is returned.
Why wrong: Method returns void.
The array remains unchanged.
Why wrong: An exception occurs before any change.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
An ArrayIndexOutOfBoundsException is thrown.
The method accesses arr[0] and arr[1] without checking the array length. When called with an array of length 1, arr[1] does not exist, so the JVM throws an ArrayIndexOutOfBoundsException at runtime. This is because Java arrays are zero-indexed and bounds checking is performed at runtime.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
An ArrayIndexOutOfBoundsException is thrown.
Why this is correct
Index 1 is out of bounds for length 1.
Related concept
Read the scenario before looking for a memorised answer.
The first element is swapped with itself.
Why it's wrong here
No swap occurs due to exception.
A new array with length 2 is returned.
Why it's wrong here
Method returns void.
The array remains unchanged.
Why it's wrong here
An exception occurs before any change.
Common exam traps
Oracle often tests the misconception that a method with a void return type will silently do nothing or leave the array unchanged, when in fact an unchecked array access throws an exception.
Detailed technical explanation
In Java, array bounds are checked at runtime by the JVM; accessing an invalid index throws ArrayIndexOutOfBoundsException, a subclass of RuntimeException. This is a common pitfall when writing utility methods that assume a minimum array length, and it highlights the importance of defensive programming with length checks (e.g., if (arr.length < 2) return;).
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Arrays and Methods — This question tests Arrays and Methods — Read the scenario before looking for a memorised answer..
The correct answer is: An ArrayIndexOutOfBoundsException is thrown. — The method accesses arr[0] and arr[1] without checking the array length. When called with an array of length 1, arr[1] does not exist, so the JVM throws an ArrayIndexOutOfBoundsException at runtime. This is because Java arrays are zero-indexed and bounds checking is performed at runtime.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. What is the output?
easyWhy C: The code initializes an array of size 5, then attempts to assign the value 99 to index 5. Since array indices in Java are zero-based, valid indices are 0 through 4. Index 5 is out of bounds, so an ArrayIndexOutOfBoundsException is thrown at runtime. Option C is incorrect because the code does not compile or output 99; it throws an exception.
Last reviewed: Jun 30, 2026
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