java-17 - Gopi Gorantala

NoClassDefFoundError vs ClassNotFoundException in Java

NoClassDefFoundError and ClassNotFoundException look interchangeable and are not. Read the frames, find the real cause, and stop the repeat throws.

Java NullPointerException: Cannot invoke ... because ... is null

Decode the helpful NullPointerException message — Cannot invoke "String.length()" because "s" is null — find the exact null reference, and fix it for good.

Java InaccessibleObjectException: Causes and --add-opens Fix

InaccessibleObjectException: module java.base does not "opens java.util" to unnamed module. Why strong encapsulation breaks reflection and how to fix it properly.

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.