There is no good reason to declare a field "public" and "static" without also declaring it "final". Most of the time this is a kludge to share a
state among several objects. But with this approach, any object can do whatever it wants with the shared state, such as setting it to
null
.
public class Greeter { public static Foo foo = new Foo(); ... }
public class Greeter { public static final Foo FOO = new Foo(); ... }