java-errors

13 Posts

Java IllegalStateException: Duplicate Key in Collectors.toMap

Collectors.toMap throws IllegalStateException: Duplicate key when two elements map to the same key. Exact causes, JDK 8-25 message differences, and the fixes.

Java UnsupportedClassVersionError: Class File Version F

java.lang.UnsupportedClassVersionError means your bytecode is newer than your JVM. Decode the class file version numbers and fix the mismatch for good.

Java OutOfMemoryError: Java Heap Space - Causes and Fixes

java.lang.OutOfMemoryError: Java heap space and GC overhead limit exceeded, explained: reproduce both, read the GC log, find the leak, and fix it properly.