With Java 5.0, the Comparable interface has been made "generic" and quite a few classes have been retro-fitted to make use of this, for example, java.math.BigDecimal now implements Comparable<BigDecimal>. Unfortunately the developers of the Java classlib forgot to preserve the old signature of compareTo with an Object argument. This means that a method has gone without any deprecation at all. Code that compiles fine in JDK 1.4 no longer compiles and no -source switch is going to help.
For example, see Castor's build in Gump:
[javac] .../src/main/org/exolab/castor/persist/ClassMolder.java:1106: compareTo(java.math.BigDecimal) in java.math.BigDecimal cannot be applied to (java.lang.Object)
[javac] if ( (o1 instanceof java.math.BigDecimal) && ((java.math.BigDecimal) o1).compareTo(o2) == 0) {
While I understand why BigDecimal can't implement Comparable<BigDecimal> and Comparable<Object> at the same time (erasure is the key), adding a compareTo(Object) method to Number would have fixed the problem for quite a few classes. I think this is a bug, but the Sun team seems to disagree - or at least think it is not significant.
This means that you need to use explicit casts in your code when you invoke compareTo. Casts that have been unnecessary in JDK 1.4.