What are Switch classes used for?

What are switch classes (derived from org.eclipse.emf.ecore.util.Switch<T>) used for?

The javadoc explains it as

An abstract base class for all switch classes.

which does not help as I have never heared about "switch classes" before.

A switch class is a class that allows you to choose and instantiates a concrete instance of a type based on a model object (in this case, an EMF model object). The examples I've seen suggest it's useful for instantiating type-specific adapters for an EMF model.

You use it by overriding the doSwitch method. For instance, say I've got a model object, and I want to instantiate an adapter object that corresponds to the type value in my model:

public class ExampleSwitch extends Switch<Adapter> {

    public Adapter doSwitch(EObject eobject) {
        if (eobject instanceof MyModel) {
            switch (eobject.getType()) {
                case TYPEA:
                    Adapter result = createTypeAAdapter(eobject);
                    if (result == null) {
                        return createDefaultAdapter(eobject);
                    }
                    return result;
                case TYPEB:
                    ...
                default:
            }
        }
    } 
}

An eclipse org.eclipse.emf.common.notify.AdapterFactory would then use this to return an Adapter.

public class MyAdapterFactory implements AdapterFactory {
    public boolean isFactoryForType(Object o) {
        return (o instanceof MyModel);
    }
    public Adapter adapt(Notifier notifier, Object type) {
        return mySwitch.doSwitch((EObject)notifier);
    }
}  

I've pulled this information from here. I haven't verified this, but apparently the EMF generator can optionally generate your AdapterFactories and Switch classes for you.