Introduction
Inheritance is an important concept in Object Oriented Programming (OOP). It is a mechanism through which an object acquires properties and behavior of another object. An object which is inheriting is called Child and other one is called Parent object. Objects belong to classes, so class having basic attributes and behavior is called Super Class (Parent class), and Class which is inheriting called Subclass (child class).
Reuseability is a very powerful feature of OOP, which is ensured through inheritance. Without inheritance a lot code is written again and again. Lets understand it by an example of vehicle.
Inheritance Example
Every vehicle has some common attributes, like name, model,company, seating capacity, production year and horse power. There are some specialized type of vehicles which have some extra attributes and behaviors than basic vehicles, like Electric vehicle has battery capacity, average per kw. Similarly Gasoline and Hybrid vehicles have specialized attributes and behaviors. Following diagram gives us a good overview.
All three type of vehicles have extra features, including basic feature of vehicle. If there is no inheritance, then we need to include all attributes and behavior of basic vehicle in all type of specialized vehicles.
Java Syntax
Java uses keyword extends to inherent a class from its superclass. Using the keyword extends, all
public attributes and behaviors are automatically included in child class, there is no need to rewrite all
the code.
Source Code
Here is the source code in java for above classes.
public class Vehicle {
String vehicle_name;
String model;
int seating_capacity;
int production_year;
float engine_horse_power;
public String getVehicle_name() {
return vehicle_name;
}
public void setVehicle_name(String vehicle_name) {
this.vehicle_name = vehicle_name;
}
public String getModel() {
return model;
}
public void setModel(String model) {
this.model = model;
}
public int getSeating_capacity() {
return seating_capacity;
}
public void setSeating_capacity(int seating_capacity) {
this.seating_capacity = seating_capacity;
}
public int getProduction_year() {
return production_year;
}
public void setProduction_year(int production_year) {
this.production_year = production_year;
}
public float getEngine_horse_power() {
return engine_horse_power;
}
public void setEngine_horse_power(float engine_horse_power) {
this.engine_horse_power = engine_horse_power;
}
}
public class Electric_vehicle extends vehicle {
float battery_capacity;
int num_of_batteries;
float fuel_average_per_kw;
public float getBattery_capacity() {
return battery_capacity;
}
public void setBattery_capacity(float battery_capacity) {
this.battery_capacity = battery_capacity;
}
public int getNum_of_batteries() {
return num_of_batteries;
}
public void setNum_of_batteries(int num_of_batteries) {
this.num_of_batteries = num_of_batteries;
}
public float getFuel_average_per_kw() {
return fuel_average_per_kw;
}
public void setFuel_average_per_kw(float fuel_average_per_kw) {
this.fuel_average_per_kw = fuel_average_per_kw;
}
}
public class Gasoline_vehicle extends vehicle {
int fuel_tank_capacity;
int slyinder_engine;
float fuel_avg_ltr;
public int getFuel_tank_capacity() {
return fuel_tank_capacity;
}
public void setFuel_tank_capacity(int fuel_tank_capacity) {
this.fuel_tank_capacity = fuel_tank_capacity;
}
public int getSlyinder_engine() {
return slyinder_engine;
}
public void setSlyinder_engine(int slyinder_engine) {
this.slyinder_engine = slyinder_engine;
}
public float getFuel_avg_ltr() {
return fuel_avg_ltr;
}
public void setFuel_avg_ltr(float fuel_avg_ltr) {
this.fuel_avg_ltr = fuel_avg_ltr;
}
}
public class Hybrid_vehicle extends vehicle {
int fuel_tank_capacity;
int engine_cylinder;
int battery_capacity;
float fuel_avg_per_ltr;
public int getFuel_tank_capacity() {
return fuel_tank_capacity;
}
public void setFuel_tank_capacity(int fuel_tank_capacity) {
this.fuel_tank_capacity = fuel_tank_capacity;
}
public int getEngine_cylinder() {
return engine_cylinder;
}
public void setEngine_cylinder(int engine_cylinder) {
this.engine_cylinder = engine_cylinder;
}
public int getBattery_capacity() {
return battery_capacity;
}
public void setBattery_capacity(int battery_capacity) {
this.battery_capacity = battery_capacity;
}
public float getFuel_avg_per_ltr() {
return fuel_avg_per_ltr;
}
public void setFuel_avg_per_ltr(float fuel_avg_per_ltr) {
this.fuel_avg_per_ltr = fuel_avg_per_ltr;
}
}
Multilevel and Multiple Inheritance
Multilevel inheritance means inheritance is at multiple level in classes. There is a parent class A, a child class B extends A and class C extends B. As C extends B, all properties and behavior of B including its parent class will also be available in class C.
public class A {………
public class B extends A{…….
public class C extends B{…….
In multiple inheritance one class can inherent more than one class at the same time. In C++ and C multiple inheritance is allowed, but in Java it is not allowed. This is because multiple inheritance can lead to ambiguity.