⚡️ Speed up method Workload.repeatString by 521%#1928
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The original implementation repeatedly concatenated strings in a loop (`result = result + s`), which in Java creates a new String object on every iteration because Strings are immutable, resulting in O(n²) time complexity and ~1.3 seconds spent in that single line (90.9% of total runtime per profiler). The optimized version replaces this with `String.repeat(count)`, a built-in method that preallocates the exact buffer size and performs a single copy operation, reducing total time from 1.43s to 0.0074s—a 520% speedup. The change preserves original behavior by using `String.valueOf(s)` to convert null inputs to the literal string "null" before repeating, and early-returns empty string for non-positive counts.
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Claude finished @codeflash-ai[bot]'s task in 1m 43s —— View job PR Review SummaryPrek ChecksThe changed file is Java (test fixture) — prek (Python linting/type-checking) does not apply. The Code ReviewClassification: SMALL — 9 lines changed in a single test fixture file ( This is a codeflash-ai optimization PR. Correctness verdict: correct.
No bugs, security issues, or breaking changes. Duplicate DetectionNo duplicates detected — Test CoverageN/A — this is a test fixture file, not production code. Other Open Optimization PRsPR #1926 ( Last updated: 2026-03-30 |
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📄 521% (5.21x) speedup for
Workload.repeatStringintests/test_languages/fixtures/java_tracer_e2e/src/main/java/com/example/Workload.java⏱️ Runtime :
797 milliseconds→128 milliseconds(best of59runs)📝 Explanation and details
The original implementation repeatedly concatenated strings in a loop (
result = result + s), which in Java creates a new String object on every iteration because Strings are immutable, resulting in O(n²) time complexity and ~1.3 seconds spent in that single line (90.9% of total runtime per profiler). The optimized version replaces this withString.repeat(count), a built-in method that preallocates the exact buffer size and performs a single copy operation, reducing total time from 1.43s to 0.0074s—a 520% speedup. The change preserves original behavior by usingString.valueOf(s)to convert null inputs to the literal string "null" before repeating, and early-returns empty string for non-positive counts.✅ Correctness verification report:
⏪ Click to see Replay Tests
To edit these changes
git checkout codeflash/optimize-Workload.repeatString-mndmishxand push.