Java Reference
In-Depth Information
All the other methods of the class have not changed and can still be called just like
before. However, this time Mammal must be declared abstract because of the walk method
on line 20. Without the abstract keyword on line 1, the Mammal class would not compile.
The following two classes shown in Figure 2.13 are valid child classes of Mammal . The
Buffalo class successfully overrides the walk method. The Feline class does not override
walk , but it is declared abstract .
1. //Buffalo.java
2. public class Buffalo extends Mammal {
3. public void walk() {
4. System.out.println(“Buffalo is walking”);
5. }
6. }
7. //Feline.java
8. public abstract class Feline extends Mammal {
9. public void sleep() {
10. System.out.println(“Feline is sleeping”);
11. }
12. }
FIGURE 2.13 Buffalo is a concrete subclass and Feline is an abstract subclass of
Mammal .
Mammal is an
abstract class.
abstract Mammal
Feline is an
abstract subclass
of Mammal.
public abstract void walk()
Buffalo
abstract Feline
public void walk()
Buffalo is a concrete
subclass of Mammal.
abstract HouseCat
HouseCat needs to
be abstract if it does
not override walk().
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