Quick Answer
The answer is the Consumer functional interface. This is correct because the Consumer<T> interface defines a single abstract method, accept(T t), which takes an argument of type T and returns void, making it the ideal choice for a lambda that processes a String without producing a return value. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your ability to match functional interfaces from the java.util.function package to lambda signatures, a common topic in the "Functional Interfaces and Lambda Expressions" objectives. A frequent trap is selecting Function<String, Void> instead, but that approach is non-idiomatic and requires explicitly returning null, whereas Consumer is purpose-built for side effects like printing or logging. To remember this, think of the name: a Consumer “consumes” its input and gives nothing back—no output, just action.
This 1Z0-829 practice question tests your understanding of working with streams and lambda expressions. Compare every option against the stated constraints before choosing — the best answer satisfies all requirements, not just the most obvious one. 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 functional interface is most appropriate for a lambda that takes a String and returns nothing?
Predicate<String>
Why wrong: Predicate returns a boolean.
Function<String, Void>
Why wrong: Function returns a value; returning Void is possible but uncommon and requires explicit null return.
Supplier<String>
Why wrong: Supplier supplies a value, takes no input.
Consumer<String>
Consumer<String> accepts a String and returns void, best suited for side-effect operations.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Consumer<String>
Option A is correct because Consumer<String> has an accept method that takes a String and returns void. Option B (Function<String, Void>) is not idiomatic; Consumer is designed for side effects.
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.
Predicate<String>
Why it's wrong here
Predicate returns a boolean.
Function<String, Void>
Why it's wrong here
Function returns a value; returning Void is possible but uncommon and requires explicit null return.
Supplier<String>
Why it's wrong here
Supplier supplies a value, takes no input.
Consumer<String>
Why this is correct
Consumer<String> accepts a String and returns void, best suited for side-effect operations.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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 1Z0-829 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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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: Consumer<String> — Option A is correct because Consumer<String> has an accept method that takes a String and returns void. Option B (Function<String, Void>) is not idiomatic; Consumer is designed for side effects.
Identify which 1Z0-829 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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