Java.io.ObjectOutputStream.writeFields() Method

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Description

The java.io.ObjectOutputStream.writeFields() method the buffered fields to the stream.

Declaration

Following is the declaration for java.io.ObjectOutputStream.writeFields() method.

public void writeFields()

Parameters

NA

Return Value

This method does not return a value.

Exception

• IOException − If I/O errors occur while writing to the underlying stream.

• NotActiveException − Called when a classes writeObject method was not called to write the state of the object.

Example

The following example shows the usage of java.io.ObjectOutputStream.writeFields() method.

package com.tutorialspoint;

import java.io.*;

public class ObjectOutputStreamDemo {
   public static void main(String[] args) {
      double d = 1.59875d;
      
      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();

         // print var of a
         System.out.println("" + a.var);
      } catch (Exception ex) {
         ex.printStackTrace();
      }
   }

   static public class Example implements Serializable {
      static int var = 76458;
      
      // assign a new serialPersistentFields 
      private static final ObjectStreamField[] serialPersistentFields = {
         new ObjectStreamField("var", Integer.TYPE)
      };

      private void readObject(ObjectInputStream in)
         throws IOException, ClassNotFoundException {

         // get the field and assign it at var
         ObjectInputStream.GetField fields = in.readFields();

         // get var
         var = fields.get("var", 0);
      }

      private void writeObject(ObjectOutputStream out) throws IOException {

         // write into the ObjectStreamField array the variable string
         ObjectOutputStream.PutField fields = out.putFields();
         fields.put("var", var);
         out.writeFields();
      }
   }
}

Let us compile and run the above program, this will produce the following result −

76458