Java IO.pdf - Nguyen Dang Binh

Java I/O
are not serializable, then the container won't be, either. Most Sun-supplied components are
serializable, but third-party components often aren't.
11.5.1.2 Problem 2: Missing a no-argument constructor in superclass
The second common problem that prevents a serializable class from being deserialized is that
a superclass of the class is not serializable and does not contain a no-argument constructor.
java.lang.Object does not implement Serializable, so all classes have at least one
superclass that's not serializable. When an object is deserialized, the no-argument constructor
of the closest superclass that does not implement Serializable is invoked to establish the
state of the object's nonserializable superclasses. If that class does not have a no-argument
constructor, then the object cannot be deserialized. For example, consider the
java.io.ZipFile class introduced in Chapter 9. It does not implement Serializable:
public class ZipFile extends Object implements java.util.zip.ZipConstants
Furthermore, it has only these two constructors, both of which take arguments:
public ZipFile(String filename) throws IOException
public ZipFile(File file) throws ZipException, IOException
Suppose you want to subclass it to allow the class to be serialized, as shown in Example 11.2.
Example 11.2. A SerializableZipFileNot
import java.io.*;
import java.util.zip.*;
public class SerializableZipFileNot extends ZipFile
implements Serializable {
public SerializableZipFileNot(String filename) throws IOException {
super(filename);
}
public SerializableZipFileNot(File file) throws IOException {
super(file);
}
public static void main(String[] args) {
try {
SerializableZipFileNot szf = new SerializableZipFileNot(args[0]);
ByteArrayOutputStream bout = new ByteArrayOutputStream();
ObjectOutputStream oout = new ObjectOutputStream(bout);
oout.writeObject(szf);
oout.close();
System.out.println("Wrote object!");
ByteArrayInputStream bin = new
ByteArrayInputStream(bout.toByteArray());
ObjectInputStream oin = new ObjectInputStream(bin);
Object o = oin.readObject();
System.out.println("Read object!");
}
catch (Exception e) {e.printStackTrace();}
}
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