advanced~3h
Coding Choices That Move the Needle
Everyday coding patterns that genuinely matter to JVM performance at scale: avoiding needless allocation in hot paths, StringBuilder versus concatenation in loops, primitive arrays versus boxed collections, and escape analysis — the JIT mechanism that sometimes lets an object skip the heap entirely — tied together with a worked before/after optimization of a realistic hot-path method.
Learning objectives
- Identify common sources of unnecessary allocation in hot-path code and explain why they cost more than they look like they should
- Explain why StringBuilder avoids the allocation cost that String concatenation incurs inside a loop
- Compare the memory layout of a primitive array against a boxed collection and quantify the overhead difference
- Explain escape analysis and the conditions under which the JIT can stack-allocate an object instead of placing it on the heap
- Apply these patterns to rewrite a realistic allocation-heavy hot-path method into a measurably leaner one
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Coding Choices That Move the Needle