ObjectOutputStream writeFields() in Java

writeFields(): This method is available in the java.io.ObjectOutputStream class of Java.

Syntax:

void java.io.ObjectOutputStream.writeFields() throws IOException

This method writes the buffered fields to the stream.

Parameters: NA

Returns: NA

Throws:

1. IOException - if I/O errors occur while writing to the underlying stream.

2. NotActiveException - Called when a class writeObject method was not called to write the state of the object.

Approach

Java

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectOutputStream;

public class ObjectOutputStreamwriteFields {
    public static void main(String[] args) throws IOException {

        FileOutputStream fileStream = new FileOutputStream("D:\\hello.txt");

        ObjectOutputStream objStream = new ObjectOutputStream(fileStream);

        objStream.writeFields();
        System.out.println("Successfully writes fields to the stream");

        objStream.close();
    }
}

Output:

Exception in thread "main" java.io.NotActiveException: no current PutField object
	at java.base/java.io.ObjectOutputStream.writeFields(ObjectOutputStream.java:484)
	at com.ObjectOutputStream.ObjectOutputStreamwriteFields.main(ObjectOutputStreamwriteFields.java:14)

Some more methods of ObjectOutputStream

close(): This method must be called to release any resources associated with the stream.

defaultWriteObject(): This method writes the non-static and non-transient fields of the current class to this stream.

flush(): This method flushes the stream.

putFields(): This method retrieves the object used to buffer persistent fields to be written to the stream.

reset(): The state is reset to be the same as a new ObjectOutputStream.

useProtocolVersion(int): This method specifies the stream protocol version to use when writing the stream.

write(byte[]): This method writes an array of bytes. 

write(int): This method writes a byte.

write(byte[], int, int): This method writes a sub array of bytes.

writeBoolean(boolean): This method writes a boolean.

writeByte(int): This method writes an 8-bit byte.

writeBytes(String): This method writes a String as a sequence of bytes.

writeChar(int): This method writes a 16-bit char.

writeChars(String): This method writes a String as a sequence of chars.

writeDouble(double): This method writes a 64-bit double.

writeFloat(float): This method writes a 32-bit float.

writeInt(int): This method writes a 32-bit int.

writeLong(long): This method writes a 64-bit long.

writeObject(Object): This method writes the specified object to the ObjectOutputStream.

writeShort(int): This method writes a 16-bit short.

writeUnshared(Object): This method writes an "unshared" object to the ObjectOutputStream.

writeUTF(String): This method is primitive data are written of this String in modified UTF-8 format.