I read some documentations about classloaders, but im still not sure where and why they are needed. The Android API says:

Loads classes and resources from a repository. One or more class loaders are installed at runtime. These are consulted whenever the runtime system needs a specific class that is not yet available in-memory.

So if i understand this correct, there can be many classlaoders which are responsible for loading new classes. But how the system decides which to use? And in which situation should a developer instantiate a new classloader?

In the Android API for Intent there is a method

public void  setExtrasClassLoader  (ClassLoader  loader)

The description says:

Sets the ClassLoader that will be used when unmarshalling any Parcelable values from the extras of this Intent.

So can i define there a special classloader so that i can pass object with an Intent which are not defined in the receiving activity? An example:

If activity A which is located in Project A (in Eclipse) defines an object which i want to send to Activity B in Project B using putExtra of the Intent object. If this object which is send over the Intent is not defined (source code in project B), then there is a NoClassDefFoundException. So can i use the method setExtraClassloader to avoid this exception? If yes, how can i decide which classloader object i have to pass? And how do I instantiate it correctly?