A lot (more than you'd expect) of Java projects and libraries depend, directly or indirectly, on the ASM library (https://en.wikipedia.org/wiki/ObjectWeb_ASM ht

A lot (more than you'd expect) of Java projects and libraries depend, directly or indirectly, on the ASM library (https://en.wikipedia.org/wiki/ObjectWeb_ASM https://en.wikipedia.org/wiki/ObjectWeb_ASM), often including a built-in renamed copy. Newer versions of Java add new functionality on the bytecode generated by the Java compiler (in a backwards compatible way, that is, newer versions of Java can fully read bytecode generated by older versions of the Java compiler), and the ASM library has to be updated to understand that new functionality. The Java bytecode verifier has also become more strict, rejecting bytecode generated by older versions of the ASM library and other bytecode generators (things like the "Illegal type in constant pool" error). And in the particular case of Java 9, they decided to deprecate several things, and quickly removed them in Java 11 (that is: with less than a year warning, and no warning if you follow only the long-term versions). That includes a lot of J2EE classes which previously came with the JRE, and now became external dependencies (with the most recent version of these external dependencies sometimes having slightly different behavior).