Java Stream vs. For Loop: Unveiling the Performance Dynamics

Java 8 introduced streams, offering code that's often more readable than traditional for loops. Despite the enhanced readability, a lingering question persists: Why might Java streams incur a performance hit compared to for loops? Let's delve into the intricacies.

Quick Conclusion

Brian Goetz, a notable figure in the Java community, emphasizes the paramount importance of code clarity and readability. For 99% of cases, prioritize clear, maintainable, and correct code. – Brian Goetz -

Performance Comparison: Readability as the Deciding Factor

The general speed differences between streams and loops aren't substantial; their pros and cons are context-dependent. Deciding between them should primarily hinge on code readability. Benchmark comparisons, provide insights into the performance nuances.

Overhead Considerations

Functional Interface Overhead: Functional interfaces use generic parameters, limiting them to reference types. Auto boxing, the conversion of primitives to references, introduces overhead. Stream API provides specialized primitive streams (e.g., IntStream) to mitigate this.

External Iterator in For Loop: For loops use an external iterator, whereas streams rely on internal iteration. Primitive types in for loops often reside in the stack, reducing overhead.

When Stream Might Outperform: Stream performance may excel when dealing with heavy functions and wrapped types, especially when iterator and functional costs are significant.

JIT compiler is optimized to for loop

The Just-In-Time (JIT) compiler tends to optimize for loops more effectively, as illustrated in the provided image. Untitled

Benchmarking Experiment by Adam Ruka

Adam Ruka conducted a benchmarking experiment comparing Java 8 Stream API and traditional for loops. Results demonstrated comparable performance, with the Stream API occasionally outperforming in specific scenarios.

He was wondering himself and wrote code to benchmark, we can see his original code on GitHub There are the result of 10,000 randomly generated Article objects on his computer.

Untitled 1 Adam Ruka’s No More Loops Benchmark result, https://www.endoflineblog.com/benchmarking-java8-streams

Result seem similar loop and stream. first one(getFirstJavaArticle()) by 16%, second one(getDistinctTags()) by 24%. The Performance of the Stream API show betters compared to for loop in some cases. Therefore, Performance issue can not be a consideration.


Other Disadvantages

  • Performance Priority: Unless your industry demands a 1% performance increase and it's a top priority, the marginal performance differences are inconsequential. Choose for loops for general use cases.

  • Debuggers: Debugging stream code might be more challenging than for loops, particularly when stepping through filters and mapping operations.

  • Cognitive Overhead: Streams should be avoided for small datasets due to unnecessary memory and CPU overhead.

  • Familiarity: In environments with specific code conventions, the familiarity of for loops might outweigh the benefits of streams.

conclusion

Java streams and for loops should prioritize code readability unless faced with a proven performance bottleneck. For most scenarios, the negligible differences in performance do not justify sacrificing code clarity. Remember Brian Goetz's advice: "Just write whatever is more readable."

reference
https://stackoverflow.com/questions/34632008/key-indicators-that-a-java-8-stream-will-run-slower-than-a-for-loop
https://www.endoflineblog.com/benchmarking-java8-streams
https://stackoverflow.com/questions/44180101/in-java-what-are-the-advantages-of-streams-over-loops
https://devm.io/java/java-performance-tutorial-how-fast-are-the-java-8-streams-118830