Polymorphism(Thinking in Java)

　　All method binding in Java uses late binding unless the method is static or final (private methods are implicitly final). This means that ordinarily you don’t need to make any decisions about whether late binding will occur—it happens automatically.

　　The result of this is that only non-private methods may be overridden, but you should watch out for the appearance of overriding private methods, which generates no compiler warnings, but doesn’t do what you might expect. To be clear, you should use a different name from a private base-class method in your derived class. 

　　If you call a dynamically-bound method inside a constructor, the overridden definition for that method is used. However, the effect of this call can be rather unexpected because the overridden method will be called before the object is fully constructed. This can conceal some difficult-to-find bugs. 

　　Java SE5 adds covariant return types, which means that an overridden method in a derived class can return a type derived from the type returned by the base-class method.