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);
}
}
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)