INHERITANCE AND POLYMORPHISM - Introduction to Java Programming: Comprehensive Version - page 420

The toString() method is defined in the GeometricObject class and modified in the Circle
class. Both methods can be used in the Circle class. To invoke the toString method defined in
the GeometricObject class from the Circle class, use super.toString() (line 7).
Can a subclass of Circle access the toString method defined in the GeometricOb-
ject class using syntax such as super.super.toString() ? No. This is a syntax error.
Several points are worth noting:

no super.super.methodName()

An instance method can be overridden only if it is accessible. Thus a private method can-
not be overridden, because it is not accessible outside its own class. If a method defined
in a subclass is private in its superclass, the two methods are completely unrelated.

override accessible instance
method

■

Like an instance method, a static method can be inherited. However, a static method
cannot be overridden. If a static method defined in the superclass is redefined in a
subclass, the method defined in the superclass is hidden. The hidden static methods
can be invoked using the syntax SuperClassName.staticMethodName .

■

cannot override static method

11.7

✓ ✓

True or false? You can override a private method defined in a superclass.

Check

11.8

Point

True or false? You can override a static method defined in a superclass.

11.9

How do you explicitly invoke a superclass's constructor from a subclass?

11.10

How do you invoke an overridden superclass method from a subclass?

11.5 Overriding vs. Overloading
Overloading means to define multiple methods with the same name but different signa-
tures. Overriding means to provide a new implementation for a method in the subclass.

Key
Point

You learned about overloading methods in Section 6.8. To override a method, the method
must be defined in the subclass using the same signature and the same return type.
Let us use an example to show the differences between overriding and overloading. In (a)
below, the method p(double i) in class A overrides the same method defined in class B . In
(b), however, the class A has two overloaded methods: p(double i) and p(int i) . The
method p(double i) is inherited from B .

public class Test {
public static void main(String[] args) {
A a = new A();
a.p( 10 );
a.p( 10.0 );
}
}

public class Test {
public static void main(String[] args) {
A a = new A();
a.p( 10 );
a.p( 10.0 );
}
}

class B {
public void p( double i) {
System.out.println(i * 2 );
}
}

class B {
public void p( double i) {
System.out.println(i * 2 );
}
}

class A extends B {
// This method overrides the method in B
public void p( double i) {
System.out.println(i);
}
}

class A extends B {
// This method overloads the method in B
public void p( int i) {
System.out.println(i);
}
}

(a) (b)