Women in Technology

Article:		Seven Low-Cost Ways to Improve Legacy Code
Subject:		using final with Serializable classes
Date:		2004-04-29 00:58:42
From:		andyp
I have a question about declaring member variables to be final in immutable classes. I agree with you that it is a trick to help the compiler enforce your own logic about the class. However when it comes to serializing these classes there is a problem. If I implement the serialization method readObject(ObjectOutputStream os), then all of the member variables that I will be setting in this method must be non-final. Do you have any suggestinos about how to have final methods in this case (without using readResolve)?

Showing messages 1 through 3 of 3.

• using final with Serializable classes
  2004-04-29 16:20:44  Robert Simmons, Jr. | [View]
  
  
  Hmm, interesting question. However, since String uses final for its data member, I immagine the problem is solvable. I will have to play around with it.
  
  I will get back to you. =)
• using final with Serializable classes
  2004-04-29 16:22:38  Robert Simmons, Jr. | [View]
  
  
  Incidentally, for those that dont know, I am Robert Simmons and Kraythe. Kraythe is my internet nickname.
• using final with Serializable classes
  2005-04-13 14:34:32  Mith [View]
  
  
  Try this on for size:
  
import java.io.Serializable;

/**
* "Typesafe enum" for the different document indicators associated with
* a transaction.
*

  
* Copyright 2003 Southwest Airlines
*/

public final class DocumentIndicator implements Serializable, Comparable
{
private static int nextOrdinal = 0;

private int ordinal;
private transient String name;

public static final DocumentIndicator SALES =
new DocumentIndicator("NA");
public static final DocumentIndicator SALES_EXCHANGES =
new DocumentIndicator("NE");
public static final DocumentIndicator POSITIVE_ADJUSTMENTS =
new DocumentIndicator("NY");
public static final DocumentIndicator TICKET_BY_MAIL_SALES =
new DocumentIndicator("TA");
public static final DocumentIndicator REFUNDS =
new DocumentIndicator("NR");
public static final DocumentIndicator NEGATIVE_ADJUSTMENTS =
new DocumentIndicator("NX");
public static final DocumentIndicator TICKET_BY_MAIL_REFUNDS =
new DocumentIndicator("TR");
public static final DocumentIndicator OLD_REFUNDS =
new DocumentIndicator("RF");

private static final DocumentIndicator[] PRIVATE_VALUES =
new DocumentIndicator[]
{
SALES, SALES_EXCHANGES, POSITIVE_ADJUSTMENTS, TICKET_BY_MAIL_SALES,
REFUNDS, NEGATIVE_ADJUSTMENTS, TICKET_BY_MAIL_REFUNDS, OLD_REFUNDS
};
/**
* All instances are controlled by the class.
*/

private DocumentIndicator(String name)
{
this.name = name;
this.ordinal = nextOrdinal++;
}
public int compareTo(Object o)
{
DocumentIndicator other = (DocumentIndicator) o;

return name.compareTo(other.name);
}
/**
* Returns the DocumentIndicator associated with the given string.
*
* @param indicator the String to try to match against the document
* indicators
* @return the DocumentIndicator associated with the given String
*/

public static DocumentIndicator getIndicatorFrom(String indicator)
{
if ("NA".equals(indicator))
{
return SALES;
}
else if ("NE".equals(indicator))
{
return SALES_EXCHANGES;
}
else if ("NY".equals(indicator))
{
return POSITIVE_ADJUSTMENTS;
}
else if ("TA".equals(indicator))
{
return TICKET_BY_MAIL_SALES;
}
else if ("NR".equals(indicator))
{
return REFUNDS;
}
else if ("NX".equals(indicator))
{
return NEGATIVE_ADJUSTMENTS;
}
else if ("TR".equals(indicator))
{
return TICKET_BY_MAIL_REFUNDS;
}
else if ("RF".equals(indicator))
{
return OLD_REFUNDS;
}
else
{
return null;
}
}
private Object readResolve() throws java.io.ObjectStreamException
{
return PRIVATE_VALUES[ordinal];
}
/**
* Returns a String that represents the value of this object.
*
* @return a string representation of the receiver
*/

public String toString()
{
return name;
}
}