1Z0-829 Working with Streams and Lambda Expressions Practice Question
A developer uses a stateful lambda in a parallel stream. Which of the following is a potential consequence?
⚠ Common exam trap
Many candidates confuse stateful lambdas with structural modification of the source, incorrectly assuming ConcurrentModificationException is the primary risk, when in fact the core issue is non-determinism from unsynchronized shared state in parallel streams.
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
✓
Non-deterministic results
Stateful lambdas (e.g., those that modify shared mutable state) in parallel streams break the non-interference and statelessness requirements of the Stream API. Because parallel streams split the source into substreams processed by multiple threads, the lack of synchronization leads to race conditions, producing non-deterministic results that vary between runs.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Non-deterministic results
Why this is correct
Correct. Stateful lambdas in parallel streams can cause race conditions, leading to non-deterministic outcomes.
- ✗
ConcurrentModificationException
Why it's wrong here
ConcurrentModificationException typically occurs when the stream source is modified, not from a stateful lambda.
- ✗
All of the above
Why it's wrong here
Only non-deterministic results are a direct consequence.
- ✗
Improved performance
Why it's wrong here
Stateful lambdas often degrade performance due to synchronization overhead.
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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