The correct answer is that a method reference can be used in place of a lambda expression of a compatible functional interface. This works because method references are simply a shorthand syntax for lambda expressions that already have a named method to execute; the compiler infers the target type from the functional interface’s single abstract method, matching its parameter list and return type to the referenced method. On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this concept tests your understanding of how to reduce boilerplate code while maintaining type safety, often appearing in questions about streams or functional interfaces like `Consumer` or `Function`. A common trap is confusing static method references with instance method references on an arbitrary object—remember that `Class::staticMethod` and `instance::method` have different parameter mappings. For a quick memory tip: think of the double colon `::` as “the method that fits this lambda’s shape,” and always verify the functional interface’s method signature matches the referenced method’s parameters.
1Z0-829 Working with Streams and Lambda Expressions Practice Question
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 TWO statements about method references are true? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Constructor references use the syntax Class::new.
Option A is correct because constructor references use the syntax `Class::new` to refer to a constructor of a class, which can be used with a functional interface whose method matches the constructor's signature. This allows creating instances without explicitly invoking `new`, leveraging the same target type inference as lambda expressions.
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.
Read the scenario before looking for a memorised answer.
✗
Array constructor references are not supported.
Why it's wrong here
Array constructor references like int[]::new are supported.
✗
Instance method references always use the keyword static.
Why it's wrong here
Instance method references use the syntax object::method, not static.
✓
A method reference can be used in place of a lambda expression of compatible functional interface.
Why this is correct
Method references are shorthand for lambdas with the same signature.
Related concept
Read the scenario before looking for a memorised answer.
✗
Method references cannot refer to methods declared in the same class.
Why it's wrong here
Methods in the same class can be referenced (e.g., this::method).
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse instance method references with static method references, mistakenly thinking the `static` keyword is required, or they overlook that array constructor references are indeed supported via `Type[]::new`.
Detailed technical explanation
How to think about this question
Under the hood, a method reference is compiled into a synthetic lambda that delegates to the referenced method, using invokedynamic to link at runtime. A subtle behavior is that instance method references on an arbitrary object of a particular type (e.g., `String::length`) require the functional interface's first parameter to be the instance, enabling concise stream operations like `map(String::length)`. In real-world scenarios, this reduces boilerplate when passing existing methods to stream pipelines or event handlers.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
Got this wrong? Here's your next step.
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 — This question tests Working with Streams and Lambda Expressions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Constructor references use the syntax Class::new. — Option A is correct because constructor references use the syntax `Class::new` to refer to a constructor of a class, which can be used with a functional interface whose method matches the constructor's signature. This allows creating instances without explicitly invoking `new`, leveraging the same target type inference as lambda expressions.
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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Question Discussion
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