Java.io.ObjectInputStream getField.defaulted() 方法

package com.codingdict;



import java.io.*;



public class ObjectInputStreamDemo implements Serializable {



   public static void main(String[] args) {

      try {



         // create a new file with an ObjectOutputStream

         FileOutputStream out = new FileOutputStream("test.txt");

         ObjectOutputStream oout = new ObjectOutputStream(out);



         // write something in the file

         oout.writeObject(new Example());

         oout.flush();

         oout.close();



         // create an ObjectInputStream for the file we created before

         ObjectInputStream ois = new ObjectInputStream(new FileInputStream("test.txt"));



         // read an object from the stream and cast it to Example

         Example a = (Example) ois.readObject();



         // get if variable string is default in Example class

         System.out.println("" + a.isDefault);



         // print the string of a

         System.out.println("" + a.string);



      } catch (Exception ex) {

         ex.printStackTrace();

      }



   }



   static public class Example implements Serializable {

      static String string = "Hello World!";

      static boolean isDefault;



      // assign a new serialPersistentFields 

      private static final ObjectStreamField[] serialPersistentFields = {

         new ObjectStreamField("string", String.class)

      };



      // create a custom readObject method

      private void readObject(ObjectInputStream in)

         throws IOException, ClassNotFoundException {



         // get the field and assign it at string variable

         ObjectInputStream.GetField fields = in.readFields();



         // check if string is defaulted, meaning if it has no value

         isDefault = fields.defaulted("string");

         string = (String) fields.get("string", null);

      }



      // create a custom writeObject method

      private void writeObject(ObjectOutputStream out) throws IOException {



         // write into the ObjectStreamField array the variable string

         ObjectOutputStream.PutField fields = out.putFields();

         fields.put("string", string);

         out.writeFields();



      }

   }

}