Java: What can and what can't be serialized?

Question

If the Serializable interface is just a Marker-Interface that is used for passing some-sort of meta-data about classes in java - I\'m a bit confused:

After reading t

Answer 1

All the primitive data types and the classes extend either Serializable directly,

class MyClass extends Serializable{
}

or indirectly,

class MyClass extends SomeClass{
}

SomeClass implements Serializable.

can be serialized. All the fields in a serializable class gets serialized except the fields which are marked transient. If a serializable class contains a field which is not serializable(not primitive and do not extend from serializable interface) then NotSerializableException will be thrown.

Answer to the second question : As @JB Nizet said. If you are going to write the instance of a class to some stream then and then only mark it as Serializable, otherwise never mark a class Serializable.