Are there any specific examples of backward incompatibilities between Java versions?

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) ?

Answer 1

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.