java-core-examples/exceptions/README.md

exceptions

Companion code for the ankurm.com post "Java Exception Handling Deep Dive: Checked vs Unchecked, Suppression, and What Exceptions Actually Cost." Module exceptions in java-core-examples.

All explanation lives in the post; this module holds the runnable evidence and the captured output.

Versions

Component	Version
JDK	25.0.4.1+1 (Temurin, LTS)
JMH	1.37
JUnit Jupiter	5.11.0
Hardware	2 vCPU x86-64 VM (timings are indicative, not a leaderboard)

Quickstart

export JDK25_HOME=/path/to/jdk-25
./scripts/run-all.sh        # rebuilds and regenerates everything in output/

What is in here

File	Shows	Output
SuppressedDemo	try/finally loses the original exception; try-with-resources suppresses the close() failure instead	01
ChainingDemo	Caused by / ... N more, and wrapping without the cause	02
CheckedVsUncheckedDemo	which types are checked; UncheckedIOException in a lambda	03
CustomHierarchyDemo	an unchecked base type with an error code; the 4-argument Throwable constructor	04
FinallyTrapDemo	return inside finally discards the exception	05
src/broken/*.java	four sources that deliberately fail to compile; javac's real message is captured	06-09
OmitStackTraceDemo	HotSpot replaces a hot implicit exception with one that has no stack trace	10
ExceptionCostBenchmark	JMH: normal vs no-stack-trace vs preallocated vs return code, at three stack depths	11
DeepTraceDemo	stack traces are capped at MaxJavaStackTraceDepth = 1024 frames	12, 14
ExceptionBehaviourTest	8 assertions behind the claims above	13

The JMH run is one fork, 3 warmup and 5 measurement iterations of 1 s; re-running moves the numbers by tens of percent but not the ordering.