Class loaders and class loading exceptions

Class loaders are responsible for loading Java classes and resources dynamically in the Java Virtual Machine at runtime. Classes are loaded into the JVM primarily on an as-needed basis. If a loaded class depends on another class, that dependent class is loaded as well. They are organized hierarchically in the following order: Java class loaders, OSGi framework class loaders, WebSphere extension class loader, application module class loader, web module class loader.

Common class loading errors include ClassNotFoundException, NoClassDefFoundError, ClassCastException, and NoSuchMethodError. Once the error is identified, there are techniques that can be applied to debug the cause of the error.