JRE upgrade to 1.4.1_04

Question

Hi,
We have a client application thats written in JAVA Swing which currently uses JRE 1.3.1. Recently the JRE version in client machines has been upgraded to 1.4.1_04.
We would like to recompile our existing application in Java 1.4.1_04. But currenly this version is not supported by Sun. Only version 1.4.2 is supported.
Could you let me know if I can complie the application in 1.4.2 and will it be backward compatible with 1.4.1_04. Or should I download the 1.4.1_04 SDK and compile my application using that.
Any suggestion would be of great help.
Thanks in advance.
Arun

Answer 1

Sun always strive to make the JVM upwards compatible, which is to say you can run old software on newer JVMs but the reverse may not be true.
The exception to this rule tends to lie in the libraries where bug fixes and API enhancements may make the new API functionally different from the old one. There is no solution to this problem from a recompilation, so there is very little point in recompiling your older application.
For example, between J2SE 1.2 and J2SE 1.3 the implementation of
java.lang.Double.hashcode
Was changed. Code depending on the old functionality will not behave the same way with the new library. A recompile cannot fix this.
Worse, an attempt to "fix" your code by recompiling it may result in a failed compilation. In 1.2 there was only one Timer class javax.swing.Timer yet in 1.3 there is another java.util.Timer.
If you use the unqualified name "Timer" in your code and use the following import statements:
import java.util.*;
import javax.swing.*;
Then your code will compile in 1.2 and not compile in 1.3 - even though the compiled code will behave as expected.
Sorry if that wasn't the answer you were expecting.
Dave.