A class may inherit from a superclass. The inherited class gains access to all public and protected aspects of the parent class. Inheritance defines an is-a relationship between classes. A child class may override anything it inherits from the parent class.
We start out with a very basic Dog class.
| code: | class Dog {
private String name;
public Dog(String initName) {
name = initName;
}
public String bark() {
return "Woof!";
}
} |
Now, we want a GuardDog class. We've already got a Dog class, so why reinvent the whole thing? Besides, a guard dog is a dog...
Assume a Person class.
| code: | class GuardDog extends Dog {
// create a constructor for this class
public GuardDog(String initName) {
// just call the parent class' constructor
super(initName);
}
public void attack(Person intruder) {
System.out.println(bark());
person.reduceHealth();
}
} |
And now, to demonstrate overriding, we create a sad MuteGuardDog class. To do this we override "bark()" so that it returns an empty string.
| code: | class MuteGuardDog extends GuardDog {
public MuteGuardDog(String initName) {
super(initName);
}
public String bark() {
return "";
}
} |
And to sum up... MuteGuardDog is a GuardDog is a Dog. This of course also means that a MuteGuardDog is a Dog.
Anywhere your program would require a Dog you could use a child of the Dog class. |
