More about inheritance - Objects First with Java: A Practical Introduction Using BlueJ - page 324

When implementing overriding methods, the super keyword can be used to invoke the super-
class version of the method. If fields or methods are declared with the protected access modi-
fier, subclasses are allowed to access them, but other classes are not.

Terms introduced in this chapter
static type, dynamic type, overriding, redefinition, method lookup, method
dispatch, method polymorphism, protected

Concept summary

■ static type The static type of a variable v is the type as declared in the source code in the

variable declaration statement.

■ dynamic type The dynamic type of a variable v is the type of the object that is currently stored in v .

■ overriding A subclass can override a method implementation. To do this, the subclass de-

clares a method with the same signature as the superclass, but with a different method body.
The overriding method takes precedence for method calls on subclass objects.

■ method polymorphism Method calls in Java are polymorphic. The same method call may at

different times invoke different methods, depending on the dynamic type of the variable used
to make that call.

■ toString Every object in Java has a toString method that can be used to return a string

representation of itself. Typically, to make it useful, a class should override this method.

■ protected Declaring a field or a method protected allows direct access to it from (direct or

indirect) subclasses.

Exercise 9.11 Assume that you see the following lines of code:

Device dev = new Printer();
dev.getName();

Printer is a subclass of Device . Which of these classes must have a definition of method
getName for this code to compile?

Exercise 9.12 In the same situation as in the previous exercise, if both classes have an
implementation of getName , which one will be executed?

Exercise 9.13 Assume that you write a class Student that does not have a declared su-
perclass. You do not write a toString method. Consider the following lines of code:

Student st = new Student();
String s = st.toString();

Will these lines compile? If so, what exactly will happen when you try to execute?