1Z0-811 Arrays and Methods Practice Question
A method is designed to reverse an array of integers. The method signature is: public static void reverse(int[] arr). The method correctly reverses the array. Which statement is true about the method?
⚠ Common exam trap
Oracle often tests the misconception that Java uses pass-by-reference for objects; the trap here is that candidates think 'pass-by-value' means the original array cannot be changed, but in reality, the reference is passed by value, allowing mutation of the array's contents.
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 modifies the original array.
The method receives a reference to the array (pass-by-value of the reference), so any modifications made to the array elements inside the method directly affect the original array object in the caller's scope. Since the method reverses the array in-place by swapping elements, the original array is mutated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
It modifies the original array.
Why this is correct
Since it returns void, the only way to provide the reversed array to the caller is by modifying the input array.
- ✗
It returns a new array that is the reverse of the input.
Why it's wrong here
The method has a void return type, so it cannot return a new array.
- ✗
It cannot be called with a null array.
Why it's wrong here
While it's true that calling with null would cause a NullPointerException, this is not the most relevant statement about the method's behavior.
- ✗
It uses pass-by-value, so the original array is unchanged.
Why it's wrong here
Pass-by-value applies to the reference; the array object itself is shared, so modifications are visible to the caller.
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Same concept, more angles
2 more ways this is tested on 1Z0-811
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. Consider a method that takes an int array and modifies it: public static void doubleArray(int[] arr) { for (int i = 0; i < arr.length; i++) { arr[i] *= 2; } }. What is the output of: int[] nums = {1, 2, 3}; doubleArray(nums); System.out.println(nums[1]);
medium- ✓ A.4
- B.8
- C.2
- D.3
Why A: The method `doubleArray` multiplies each element of the array by 2. The array `nums` is passed by reference, so modifications inside the method affect the original array. After execution, `nums[1]` (originally 2) becomes 4, which is printed.
Variation 2. Which TWO methods correctly modify the passed array in place?
medium- ✓ A.public void zeroOut(int[] a) { for (int i = 0; i < a.length; i++) a[i] = 0; }
- ✓ B.public void incrementEach(int[] a) { for (int i = 0; i < a.length; i++) a[i]++; }
- C.public void reset(int[] a) { a = new int[10]; }
- D.public void swap(int[] a) { int[] temp = a; a = new int[1]; a[0] = temp[0]; }
- E.public void setFirst(int[][] a) { a = new int[1][1]; a[0][0] = 5; }
Why A: It directly modifies each element of the passed array by assigning 0 to a[i] within the loop. In Java, when an array is passed to a method, the method receives a reference to the same array object, so changes to the array's elements are reflected in the caller's array.
JA
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Senior Network & Security Engineer · founder of Courseiva
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