1Z0-829 Working with Streams and Lambda Expressions Practice Question
A developer wants to compute the product of all even numbers in a stream of integers. Which of the following correctly implements this using streams?
⚠ Common exam trap
The trap here is that candidates often forget the identity value must be the neutral element for the reduction operation, so they pick Option B with identity 0 for multiplication, or they skip filtering entirely and pick Option C, thinking the product of all numbers is sufficient.
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
✓
filter(n -> n % 2 == 0).reduce(1, (a, b) -> a * b)
It first filters the stream to keep only even numbers (n % 2 == 0), then uses reduce with an identity of 1 and a multiplication lambda (a, b) -> a * b. The identity 1 is the neutral element for multiplication, ensuring that if no even numbers exist, the result is 1 rather than an error or incorrect value.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
reduce(1, (a, b) -> (a % 2 == 0) ? a * b : a)
Why it's wrong here
The lambda is not a valid BinaryOperator; it conditionally multiplies, but reduce expects a function that is applied uniformly to pairs of elements. This will produce incorrect results.
- ✗
filter(n -> n % 2 == 0).reduce(0, (a, b) -> a * b)
Why it's wrong here
Identity 0 causes the product to always be 0, which is incorrect.
- ✗
reduce(1, (a, b) -> a * b)
Why it's wrong here
This multiplies all elements together, ignoring the even condition.
- ✓
filter(n -> n % 2 == 0).reduce(1, (a, b) -> a * b)
Why this is correct
Correct. Filter ensures only even numbers are processed, then reduction multiplies them using identity 1.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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