Are there any specific examples of backward incomp

Question

Have there been incompatibilities between Java releases where Java source code/Java class files targeting Java version X won't compile/run under version Y (where Y > X) ?

By "Java release" I mean versions such as:

• JDK 1.0 (January, 1996)
• JDK 1.1 (February, 1997)
• J2SE 1.2 (December, 1998)
• J2SE 1.3 (May, 2000)
• J2SE 1.4 (February, 2002)
• J2SE 5.0 (September, 2004)
• Java SE 6 (December, 2006)

House rules:

• Please include references and code examples where possible.
• Please try to be very specific/concrete in your answer.
• A class that is being marked as @Deprecated does not count as a backwards incompatibility.

Answer 1

Every release of Swing broke something for us, from 1.3 through 1.6.

The JDBC issue has already been mentioned, but existing code worked.

From 1.5 to 1.6 there was a change in the behavior of Socket which broke the Cisco client.

Of course new reserved keywords were introduced.

The big one which I think was truely unforgivable on Sun's part was System.getenv(). It worked in 1.0, and then was deprecated and changed to throw an error on all platforms under the rather dubious justification that the Mac didn't have system environment variables. Then the Mac got system environment variables, so in 1.5 it was undeprecated and works. There is no reasonable justification for doing that. Return an empty set on a Mac (Swing has much bigger cross-platform issues if you want to care about that level of cross platform consistency) or even on all platforms.

I never agreed with them turning off the feature, but to change it to throw an error was just a pure breaking change that if they were going to do, they should have just removed the method entirely.

But, really from 1.0 to 1.1 they were less concerned about backwards compatability. For example, they dropped "private protected" as a modifier.

So the upshot is that every version changes enough to require close evaluation, that is why you still see many 1.4 questions here on SO.

Answer 2

Between 1.3 and 1.4 the interpretation of Long.parseLong(String) handled the empty string differently. 1.3 returns a 0 value, whereas 1.4 throws a NumberFormatException.

Recompiles aren't needed, but working code stopped working if it relied on the 1.3 behaviour.