Java 1.4 under Java 1.6?

[Jochen Rittmann]

Hello,
can i run an J2EE Application which is written under Java 1.4 in Java 1.6. Only compile 1.6 and then run?
Is there a official documentation about this theme?
Thank you,
Jochen

[Pushkar Choudhary]

Java does have good backward compatibility. Refer to this on the Sun Java website regarding compatibility.

[Jesper de Jong]

Each version of the JDK comes with information about backward compatibility, Pushkar provided you already with a link for Java 6.

Backward compatibility has always been very important for Java. Normally you should not have any problems running old applications on a new version of Java. You do not even need to recompile the code - the old compiled classes should run fine. But you should test it first with your particular application - some programmers use unofficial APIs or other techniques that make their programs incompatible with newer versions of Java, it's impossible to guarantee 100% that everything will work.

[Rob Spoor]

There are two reasons a program may break when upgrading your JVM:

1) programmers have used undocumented classes, like those in package that start with sun, sunw or com.sun. These classes can change or even disappear even between minor JVM updates.

2) there was a bug in the API at the earlier version, and the programmer has created a workaround. That workaround now causes bugs in the code since it is no longer needed.


The first one is much more frequent though.

[W. Joe Smith]

And, if I recall correctly, there were some new reserved words between 1.4 and 1.6, such as enum. I'm not sure how much of a problem that will cause, but I believe it has been discussed on here before.

[Wouter Oet]

Yes that is true however that is only a problem at compile-time:

Compile with 1.6: javac -source 1.4 Test.java --> Only a warning

int enum = 5;

Run with 1.6 java Test --> No error/exception