Quick Answer
The answer is option C, (a, b) -> return a + b, because it is syntactically invalid. In Java, a lambda expression with an expression body—meaning no curly braces—cannot contain the return keyword; the expression itself is implicitly returned. When you use a block body, denoted by braces, return is required, but without braces, its presence causes a compilation error. This question tests your understanding of lambda body syntax, a frequent pitfall on the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, where the examiners love to disguise invalid syntax by mixing expression and block body rules. A common trap is assuming return is always needed, but remember: no braces, no return. For a quick memory tip, think of it as "braces bring back return"—if you see braces, you must use return; if you see no braces, you must omit it.
This 1Z0-829 practice question tests your understanding of working with streams and lambda expressions. 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 of the following lambda expressions is syntactically invalid?
() -> {return 42;}
Why wrong: Valid. Block body with return statement.
(a, b) -> a + b
Why wrong: Valid. Type inference with single expression.
(a, b) -> return a + b;
Invalid. 'return' keyword requires a block body (curly braces).
(int a, int b) -> a + b
Why wrong: Valid. Explicit parameter types with single expression body.
(a) -> a * 2
Why wrong: Valid. Single parameter with expression body.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
(a, b) -> return a + b;
Option C is syntactically invalid because in a lambda expression, the `return` keyword is only allowed inside a block body (with braces). When using an expression body (no braces), the `return` keyword must be omitted, and the expression itself is implicitly returned. Option C incorrectly uses `return` without braces, which is a syntax error.
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.
() -> {return 42;}
Why it's wrong here
Valid. Block body with return statement.
(a, b) -> a + b
Why it's wrong here
Valid. Type inference with single expression.
(a, b) -> return a + b;
Why this is correct
Invalid. 'return' keyword requires a block body (curly braces).
Related concept
Read the scenario before looking for a memorised answer.
(int a, int b) -> a + b
Why it's wrong here
Valid. Explicit parameter types with single expression body.
(a) -> a * 2
Why it's wrong here
Valid. Single parameter with expression body.
Common exam traps
The trap here is that candidates often confuse the syntax of expression lambdas with block lambdas, mistakenly thinking `return` can be used without braces, or they forget that a single expression without `return` is implicitly returned.
Detailed technical explanation
Lambda expressions in Java have two forms: expression lambdas (e.g., `(a, b) -> a + b`) and block lambdas (e.g., `(a, b) -> { return a + b; }`). The `return` keyword is only valid inside a block lambda. Under the hood, the compiler desugars lambdas into invokedynamic calls, and the syntax rules are enforced at compile time. A real-world scenario where this matters is when writing concise stream pipelines; using `return` incorrectly can cause compilation failures that are easy to miss.
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
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Working with Streams and Lambda Expressions — study guide chapter
Learn the concepts, then practise the questions
Working with Streams and Lambda Expressions practice questions
Targeted practice on this topic area only
All 1Z0-829 questions
509 questions across all exam domains
Oracle Certified Professional Java SE 17 Developer 1Z0-829 study guide
Full concept coverage aligned to exam objectives
1Z0-829 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Practise 1Z0-829 questions linked to Handling Date, Time, Text, Numeric and Boolean Values.
Practise 1Z0-829 questions linked to Controlling Program Flow.
Practise 1Z0-829 questions linked to Utilizing Java Object-Oriented Approach.
Practise 1Z0-829 questions linked to Handling Exceptions.
Practise 1Z0-829 questions linked to Working with Arrays and Collections.
Practise 1Z0-829 questions linked to Working with Streams and Lambda Expressions.
Practise 1Z0-829 questions linked to Java Platform Overview and Packaging.
Practise 1Z0-829 questions linked to Java I/O API and Securing Applications.
Practise 1Z0-829 questions linked to 1Z0-829 fundamentals.
Practise 1Z0-829 questions linked to 1Z0-829 scenario.
Practise 1Z0-829 questions linked to 1Z0-829 troubleshooting.
Practice this exam
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Working with Streams and Lambda Expressions — This question tests Working with Streams and Lambda Expressions — Read the scenario before looking for a memorised answer..
The correct answer is: (a, b) -> return a + b; — Option C is syntactically invalid because in a lambda expression, the `return` keyword is only allowed inside a block body (with braces). When using an expression body (no braces), the `return` keyword must be omitted, and the expression itself is implicitly returned. Option C incorrectly uses `return` without braces, which is a syntax error.
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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 25, 2026
This 1Z0-829 practice question is part of Courseiva's free Oracle certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 1Z0-829 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.