Question 399 of 519

Utilizing Java Object-Oriented Approach →hardMultiple SelectObjective-mapped

Sealed Class Inheritance Rules — Permits Clause and Subclass Restrictions

This 1Z0-829 practice question tests your understanding of utilizing java object-oriented approach. 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.

Which TWO statements are true about the sealed class feature in Java 17?

A
A sealed class restricts which other classes or interfaces may extend or implement it.
This statement is true because a sealed class restricts which classes may extend it by using the `permits` clause to list the allowed subclasses.
B
A sealed interface cannot use the permits clause.
Why wrong: This statement is false because a sealed interface can indeed use the `permits` clause to specify which classes can implement it.
C
A subclass of a sealed class must be declared as final, sealed, or non-sealed.
This statement is correct. Any subclass of a sealed class must be declared with one of three modifiers: `final`, `sealed`, or `non-sealed`.
D
The permits clause must list all direct subclasses of a sealed class.
Why wrong: This statement is false. The `permits` clause is not mandatory if the sealed class and its direct subclasses are declared in the same compilation unit. Additionally, even when used, it must list all permitted subclasses, but it is not always required.
E
A sealed class must be declared as abstract.
Why wrong: This statement is false. A sealed class can be concrete (non-abstract). For example, a sealed class can be instantiated.

Full breakdown with real-world context →

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

✓

A sealed class restricts which other classes or interfaces may extend or implement it.

Option A is correct because the primary purpose of the sealed class feature is to explicitly control which other classes or interfaces are permitted to extend or implement it. This is achieved by using the `permits` clause to list the allowed subclasses, thereby restricting the inheritance hierarchy.

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.

✓
A sealed class restricts which other classes or interfaces may extend or implement it.
Why this is correct
This statement is true because a sealed class restricts which classes may extend it by using the `permits` clause to list the allowed subclasses.
Related concept
Read the scenario before looking for a memorised answer.
✗
A sealed interface cannot use the permits clause.
Why it's wrong here
This statement is false because a sealed interface can indeed use the `permits` clause to specify which classes can implement it.
✓
A subclass of a sealed class must be declared as final, sealed, or non-sealed.
Why this is correct
This statement is correct. Any subclass of a sealed class must be declared with one of three modifiers: `final`, `sealed`, or `non-sealed`.
Related concept
Read the scenario before looking for a memorised answer.
✗
The permits clause must list all direct subclasses of a sealed class.
Why it's wrong here
This statement is false. The `permits` clause is not mandatory if the sealed class and its direct subclasses are declared in the same compilation unit. Additionally, even when used, it must list all permitted subclasses, but it is not always required.
✗
A sealed class must be declared as abstract.
Why it's wrong here
This statement is false. A sealed class can be concrete (non-abstract). For example, a sealed class can be instantiated.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often confuse the requirements for subclasses of a sealed class, mistakenly thinking they must be `final` only, or they overlook that a sealed class can be concrete and does not need to be abstract.

Detailed technical explanation

How to think about this question

Under the hood, the sealed class feature enforces compile-time checks that ensure no unauthorized subclass exists outside the permits list, and the compiler generates a sealed descriptor in the class file. A real-world scenario is modeling a payment method hierarchy where only specific payment types (e.g., CreditCard, PayPal) are allowed, preventing arbitrary extensions that could break business logic.

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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.

What to study next

Got this wrong? Here's your next step.

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FAQ

Questions learners often ask

What does this 1Z0-829 question test?

Utilizing Java Object-Oriented Approach — This question tests Utilizing Java Object-Oriented Approach — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: A sealed class restricts which other classes or interfaces may extend or implement it. — Option A is correct because the primary purpose of the sealed class feature is to explicitly control which other classes or interfaces are permitted to extend or implement it. This is achieved by using the `permits` clause to list the allowed subclasses, thereby restricting the inheritance hierarchy.

What should I do if I get this 1Z0-829 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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Same concept, more angles

1 more ways this is tested on 1Z0-829

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. Which statement about the code is correct?

hard

✓ A.A compilation error occurs in the Triangle class because Triangle is not listed in the permits clause.
B.A compilation error occurs because Circle must be declared final.
C.A compilation error occurs because Shape must be declared abstract.
D.The code compiles successfully.

Why A: Option A is correct because in a sealed class hierarchy, the `permits` clause must list all direct subclasses. If `Triangle` extends `Shape` but is not listed in the `permits` clause of `Shape`, the compiler will report an error. The sealed class mechanism enforces that only explicitly permitted subclasses may extend the sealed class.

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