Java Is Fast. Your Code Might Not Be.
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A Java order-processing demo app was optimized from 1,198ms to 239ms (5x throughput, 87% less heap, 79% fewer GC pauses) by fixing eight common anti-patterns. The patterns covered are: string concatenation in loops causing O(n²) copies, accidental O(n²) stream iteration inside loops, String.format() in hot paths, autoboxing
Table of contents
1. String Concatenation in Loops #2. Accidental O(n²) with Streams Inside Loops #3. String.format() in Hot Paths #4. Autoboxing in Hot Paths #5. Exceptions for Control Flow #6. Too-Broad Synchronization #7. Repeated Creation of “Reusable” Objects #8. Virtual Thread Pinning (If You’re on JDK 21–23) #The Compounding Effect #Sort: