How not to implement Comparable

I have already blogged about the danger of numeric overflows. I recently came across this example in Java course materials (!!!):

public class Foo implements Comparable<Foo> {
private int number;
public int compareTo(Foo o) {
  if (this == o) return 0;
  return number - o.number;
}
}

How do you think Integer.MAX_VALUE compares to negative numbers? It will appear smaller. This reminds me of even worse case we encountered in a real codebase. Look at this:

public class Foo implements Comparable<Foo> {
private long id;
//...
public int compareTo(Foo o) {
  if (this == o) return 0;
  return (int)(id - o.id);
}
public boolean equals(Object o) {
  return o != null && (o instanceOf Foo) && compareTo((Foo)o) == 0;
}
}

How do you think new Foo(8325671243L) and new Foo(25505540427L) compare? They are equal, but I will do it ala Weiqi Gao and leave you to find out why... :-)