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

1. Serialization ignores static fields, because they are not part of ay particular state state.

2. Base class fields are only hendled if the base class itself is serializable.

3. Transient fields.

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 resons 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.

An error is an irrecoverable condition occurring at runtime. Such as OutOfMemory error.

These JVM errors and you can not repair them at runtime. While exceptions are conditions that occur because of bad input etc. Example: FileNotFoundException will be thrown if the specified file does not exist. Or a NullPointerException will take place if you try using a null reference.

In most of the cases it is possible to recover from an exception (probably by giving user a feedback for entering proper values etc.).