There are three exceptions in which serialization doesnot necessarily read and write to the stream. These are

No, there is not sizeof operator in Java. So there is not direct way to determine the size of an object directly in Java.

Java provides specialized classes corresponding to each of the primitive data types. These are called wrapper classes.
They are example: Integer, Character, Double etc.

It is sometimes easier to deal with primitives as objects. Moreover most of the collection classes store objects and not primitive data types. And also the wrapper classes provide many utility methods also.
Because of these reasons we need wrapper classes. And since we create instances of these classes we can store them in any of the collection classes and pass them around as a collection. Also we can pass them around as method parameters where a method expects an object.

Checked exception are those which the Java compiler forces you to catch.
Example: IOException are checked exceptions.