Why Conditionalonclass does not have ClassNotFound class loading exception in spring boot

When viewing the original code there are a lot of red places, where these import failed, why did not error when running?

First, these @configuration classes are not referenced by the class in the program to the

Second, even if you refer to this class, you do not necessarily refer to a specific method in the class. Check out the Spring class loader's original code??

Although these places import failed, but did not affect. Class loading,

This means that the jars that are dependent on compiling these @configuration classes must exist , but these jars can not be supplied at runtime

Why Conditionalonclass does not have ClassNotFound class loading exception in spring boot