Quick Answer
The correct answer is that an ArrayStoreException is thrown at runtime. This occurs because Java arrays are covariant, meaning an `Integer[]` can be assigned to an `Object[]` variable, but the array’s actual runtime component type remains `Integer`. When you attempt to store a `String` into that array, the Java Virtual Machine checks the type at runtime and throws an ArrayStoreException, as the stored type is incompatible with the array’s concrete element type. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this concept tests your understanding of array covariance and runtime type safety—a common trap where developers mistakenly think the compile-time reference type (`Object[]`) determines what can be stored. Remember the memory tip: “Arrays know their real type at runtime, not just their reference type.”
This 1Z0-829 practice question tests your understanding of working with arrays and collections. 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.
What will be the result of the following code? Object[] arr = new Integer[5]; arr[0] = "String";
Successfully stores "String"
Why wrong: Array is Integer[].
ArrayStoreException at runtime
Runtime type is Integer[], incompatible.
Compilation error
Why wrong: Line compiles: Object[] can hold String.
ClassCastException
Why wrong: ArrayStoreException is thrown.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
ArrayStoreException at runtime
The code creates an array of type `Integer[]` referenced by an `Object[]` variable. At runtime, the array's actual component type is `Integer`, so attempting to store a `String` violates the array's type constraint and throws an `ArrayStoreException`.
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.
Successfully stores "String"
Why it's wrong here
Array is Integer[].
ArrayStoreException at runtime
Why this is correct
Runtime type is Integer[], incompatible.
Related concept
Read the scenario before looking for a memorised answer.
Compilation error
Why it's wrong here
Line compiles: Object[] can hold String.
ClassCastException
Why it's wrong here
ArrayStoreException is thrown.
Common exam traps
The trap here is that candidates see the reference type `Object[]` and assume the array can hold any `Object`, forgetting that the actual runtime type of the array object determines what can be stored, leading them to pick Option A or D.
Detailed technical explanation
Under the hood, Java arrays are covariant and reified: the array object at runtime remembers its exact component type (e.g., `Integer`). The `astore` bytecode instruction includes a check that the value's type is assignment-compatible with the array's actual component type; if not, `ArrayStoreException` is thrown. This design prevents heap pollution while allowing polymorphic array references, a trade-off that can lead to subtle bugs in generic-like code.
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 1Z0-829 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
Working with Arrays and Collections — This question tests Working with Arrays and Collections — Read the scenario before looking for a memorised answer..
The correct answer is: ArrayStoreException at runtime — The code creates an array of type `Integer[]` referenced by an `Object[]` variable. At runtime, the array's actual component type is `Integer`, so attempting to store a `String` violates the array's type constraint and throws an `ArrayStoreException`.
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 25, 2026
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