Quick Answer
The answer is double[] transactions = new double[31]; because this is the correct array declaration syntax in Java for creating an array of 31 double values, where the size is specified after the new keyword and the brackets appear before the variable name. This syntax allocates contiguous memory for 31 double elements, each automatically initialized to 0.0, with valid indices ranging from 0 to 30. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of array instantiation versus declaration—a common trap is confusing int[] arr = new int[5]; with int arr[] = new int[5]; (both are valid, but the former is preferred for readability). Another frequent mistake is omitting the size or using a non-integer literal, which causes a compilation error. To remember, think: "new double[size]" is the instantiation step that actually creates the array object; without it, you only have a reference variable. A useful mnemonic is "Declare with brackets, create with new and a number."
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.
A banking application stores daily transaction amounts in an array. Which declaration correctly creates an array of 31 double values?
double[] transactions = new double[31];
Correct syntax: declares array and allocates 31 elements.
double transactions[] = new double[30];
Why wrong: Only allocates 30 elements, not 31.
int[] transactions = new int[31];
Why wrong: Data type should be double, not int.
double[] transactions = new double[];
Why wrong: Missing size; compilation error.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
double[] transactions = new double[31];
Option A is correct because it uses the proper syntax to declare an array of double values and initializes it with a size of 31, which allocates memory for 31 double elements, each defaulting to 0.0. In Java, the array size must be specified when using the 'new' keyword, and the index range is 0 to 30, accommodating exactly 31 daily transaction amounts.
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.
double[] transactions = new double[31];
Why this is correct
Correct syntax: declares array and allocates 31 elements.
Related concept
Read the scenario before looking for a memorised answer.
double transactions[] = new double[30];
Why it's wrong here
Only allocates 30 elements, not 31.
int[] transactions = new int[31];
Why it's wrong here
Data type should be double, not int.
double[] transactions = new double[];
Why it's wrong here
Missing size; compilation error.
Common exam traps
Oracle often tests the distinction between array size and index range, tricking candidates into choosing an array of size 30 (index 0-29) when 31 elements are needed, or confusing the data type (int vs double) for monetary values.
Detailed technical explanation
In Java, array declaration and initialization can be combined as 'double[] transactions = new double[31];', which creates a contiguous block of memory for 31 double-precision floating-point values (each 8 bytes, totaling 248 bytes). The array's length is fixed at creation time and cannot be changed, making it ideal for a fixed number of daily entries. Under the hood, the JVM stores the array length in the object header, and accessing an index out of bounds throws an ArrayIndexOutOfBoundsException at runtime.
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: double[] transactions = new double[31]; — Option A is correct because it uses the proper syntax to declare an array of double values and initializes it with a size of 31, which allocates memory for 31 double elements, each defaulting to 0.0. In Java, the array size must be specified when using the 'new' keyword, and the index range is 0 to 30, accommodating exactly 31 daily transaction amounts.
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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Last reviewed: Jun 30, 2026
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