What is the class called that is inheriting the properties of another class?

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);   } }

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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.

Inheritance allows us to define a class that inherits all the methods and properties from another class.

Parent class is the class being inherited from, also called base class.

Child class is the class that inherits from another class, also called derived class.

Create a Parent Class

Any class can be a parent class, so the syntax is the same as creating any other class:

Example

Create a class named Person, with firstname and lastname properties, and a printname method:

class Person:
  def __init__(self, fname, lname):
    self.firstname = fname
    self.lastname = lname

  def printname(self):
    print(self.firstname, self.lastname)

#Use the Person class to create an object, and then execute the printname method:

x = Person("John", "Doe")
x.printname()

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Create a Child Class

To create a class that inherits the functionality from another class, send the parent class as a parameter when creating the child class:

Example

Create a class named Student, which will inherit the properties and methods from the Person class:

class Student(Person):
  pass

Note: Use the pass keyword when you do not want to add any other properties or methods to the class.

Now the Student class has the same properties and methods as the Person class.

Example

Use the Student class to create an object, and then execute the printname method:

x = Student("Mike", "Olsen")
x.printname()

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Add the __init__() Function

So far we have created a child class that inherits the properties and methods from its parent.

We want to add the __init__() function to the child class (instead of the pass keyword).

Note: The __init__() function is called automatically every time the class is being used to create a new object.

Example

Add the __init__() function to the Student class:

class Student(Person):
  def __init__(self, fname, lname):
    #add properties etc.

When you add the __init__() function, the child class will no longer inherit the parent's __init__() function.

Note: The child's __init__() function overrides the inheritance of the parent's __init__() function.

To keep the inheritance of the parent's __init__() function, add a call to the parent's __init__() function:

Example

class Student(Person):
  def __init__(self, fname, lname):
    Person.__init__(self, fname, lname)

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Now we have successfully added the __init__() function, and kept the inheritance of the parent class, and we are ready to add functionality in the __init__() function.

Use the super() Function

Python also has a lastname1 function that will make the child class inherit all the methods and properties from its parent:

Example

class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)

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By using the lastname1 function, you do not have to use the name of the parent element, it will automatically inherit the methods and properties from its parent.

Add Properties

Example

Add a property called lastname3 to the Student class:

class Student(Person):
  def __init__(self, fname, lname):
    super().__init__(fname, lname)
    self.graduationyear = 2019

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In the example below, the year lastname5 should be a variable, and passed into the Student class when creating student objects. To do so, add another parameter in the __init__() function:

Example

Add a lastname7 parameter, and pass the correct year when creating objects:

class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

x = Student("Mike", "Olsen", 2019)

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Add Methods

Example

Add a method called lastname8 to the Student class:

class Student(Person):
  def __init__(self, fname, lname, year):
    super().__init__(fname, lname)
    self.graduationyear = year

  def welcome(self):
    print("Welcome", self.firstname, self.lastname, "to the class of", self.graduationyear)

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If you add a method in the child class with the same name as a function in the parent class, the inheritance of the parent method will be overridden.

Test Yourself With Exercises

Exercise:

What is the correct syntax to create a class named Student that will inherit properties and methods from a class named Person?

What is the name of a class inheriting properties of another class?

What is an inherited class called?

What does it mean when a class inherits from another class?