Input and Output - Java - page 415

os . writeObject ( theGraph );
os . close ();

}

public public void throws IOException , ClassNotFoundException {

ObjectInputStream is = new

void dump () throws

new ObjectInputStream (

new FileInputStream ( FILENAME ));
System . out . println ( is . readObject ());
is . close ();

new

}

}

See Also

For more on the standard Serialization, see the chapter on this topic in Effective Java .

Preventing ClassCastExceptions with SerialVersionUID

Problem

Your classes were recompiled, and you're getting ClassCastException s that you shouldn't.

Solution

Run serialver to generate a “serial version UUID” and paste its output into your classes
before you start. Or use your IDE's tools for this purpose.

Discussion

When a class is undergoing a period of evolution—particularly a class being used in a net-
working context such as RMI or servlets—it may be useful to provide a serialVersionUID
value in this class. This is a long that is basically a hash of the methods and fields in the
class. Both the object serialization API (see Saving and Restoring Java Objects ) and the
JVM, when asked to cast one object to another (common when using collections, as in
Chapter 7 ) , either look up or, if not found, compute this value. If the value on the source and
destination do not match, a ClassCastException is thrown. Most of the time, this is the cor-
rect thing for Java to do.