According to the JVM Instruction Set, ARRAYLENGTH pops a value from the stack
and pushes a value to the stack. In BCEL, it only implements StackProducer, so
it creates an incorrectly high stack height. The Constants class already has the
correct value for it, but since the instruction does not implement StackConsumer
it is never used. The easiest solution is to change
src\java\src\java\org\apache\bcel\generic\ARRAYLENGTH.java to implement
StackConsumer. This will fix the bug.

I didn't attach a patch for this because the change is so tiny.