Inheritance

Inheritance is a way to create a relationship between classes so a Child class can reuse the attributes and methods of a Parent class.

• Parent class: holds common features.
• Child class: shares the parent's features, and adds its own.

Real World Example: Employee

A PartTimeEmployee is also an Employee. This is called an "is a" relationship.

• PartTimeEmployee is an Employee.
• Both share common things: name, email, work().
• PartTimeEmployee also has its own feature: workingHours.

Inheritance in Java

class Employee {
    String name;
    String email;

    public void work() {
        System.out.println("Working...");
    }
}

class PartTimeEmployee extends Employee {
    int workingHours;
}

extends is the keyword used to inherit a class in Java. PartTimeEmployee automatically gets name, email, and work() from Employee, without rewriting them, and still defines its own workingHours.

Class Diagram

┌───────────────────────┐
│       Employee        │
├───────────────────────┤
│ name                  │
│ email                 │
│ work()                │
└───────────────────────┘
            ▲
            │ extends
┌───────────────────────┐
│   PartTimeEmployee     │
├───────────────────────┤
│ workingHours          │
└───────────────────────┘

The arrow points from the child class up to the parent class it extends. PartTimeEmployee inherits everything Employee has, and adds workingHours on top.

Exam Focus Points

• Inheritance lets a child class reuse a parent class's attributes and methods through the extends keyword.
• The relationship between parent and child is described as "is a": PartTimeEmployee is an Employee.
• A child class can still add its own extra attributes or methods on top of what it inherits.

Summary

• Inheritance creates a parent and child relationship between classes so common features can be shared.
• The child class uses extends to inherit the parent's attributes and methods without rewriting them.
• The child class can still define its own additional attributes and methods.
• Inheritance = "is a" relationship + sharing common features.