Tóm Tắt
Java
Inheritance
Java Inheritance (Subclass and Superclass)
In Java, it is possible to inherit attributes and methods from one class to another. We group the “inheritance concept” into two categories:
- subclass (child) – the class that inherits from another class
- superclass (parent) – the class being inherited from
To inherit from a class, use the extends
keyword.
In the example below, the Car
class
(subclass) inherits the attributes and methods from the Vehicle
class
(superclass):
Example
class Vehicle {
protected String brand = "Ford"; // Vehicle attribute
public void honk() { // Vehicle method
System.out.println("Tuut, tuut!");
}
}
class Car extends Vehicle {
private String modelName = "Mustang"; // Car attribute
public static void main(String[] args) {
// Create a myCar object
Car myCar = new Car();
// Call the honk() method (from the Vehicle class) on the myCar object
myCar.honk();
// Display the value of the brand attribute (from the Vehicle class) and the value of the modelName from the Car class
System.out.println(myCar.brand + " " + myCar.modelName);
}
}
Try it Yourself »
Did you notice the protected
modifier in Vehicle?
We set the brand attribute in Vehicle to a protected
access
modifier. If it was set to private
, the Car class would not be able to access
it.
Why And When To Use “Inheritance”?
– It is useful for code reusability: reuse attributes and methods of an existing class when you create a new class.
Tip: Also take a look at the next chapter, Polymorphism, which uses inherited methods to perform different tasks.
The final Keyword
If you don’t want other classes to inherit from a class, use the final
keyword:
If you try to access a final
class, Java will generate an error:
final class Vehicle {
...
}
class Car extends Vehicle {
...
}
The output will be something like this:
Main.java:9: error: cannot inherit from final Vehicle
class Main extends
Vehicle {
^
1 error)
Try it Yourself »