Inheritance1

Inheritance
• Inheritance in java is a mechanism in which one
object acquires all the properties and behaviors
of parent object
• The idea behind inheritance in java is that you
can create new classes that are built upon
existing classes. When you inherit from an
existing class, you can reuse methods and fields
of parent class, and you can add new methods
and fields also.
• Inheritance represents the IS-A relationship, also
known as parent-child relationship.

Why use inheritance in java
• For Method Overriding (so runtime
polymorphism can be achieved).
• For Code Reusability.
• Syntax of Java Inheritance
class Subclass-name extends Superclass-name
{
//methods and fields
}
The extends keyword indicates that you are making a
new class that derives from an existing class.

Example
• As displayed in the above figure, Programmer is the subclass and Employee is the
superclass. Relationship between two classes is Programmer IS-A Employee.It
means that Programmer is a type of Employee.
• In the above example, Programmer object can access the field of own class as
well as of Employee class i.e. code reusability.
class Employee{
float salary=40000;
}
class Programmer extends Employee{
int bonus=10000;
public static void main(String args[]){
Programmer p=new Programmer();
System.out.println("Programmer salary is:"+p.salary);
System.out.println("Bonus of Programmer is:"+p.bonus);
}
}
Output:
Programmer salary is:40000.0
Bonus of programmer is:10000

super keyword in java
• The super keyword in java is a reference variable that is
used to refer immediate parent class object.
• Whenever you create the instance of subclass, an
instance of parent class is created implicitly i.e.
referred by super reference variable.
• Usage of java super Keyword
– super is used to refer immediate parent class instance
variable.
– super() is used to invoke immediate parent class
constructor.
– super is used to invoke immediate parent class method.

• super is used to refer immediate parent class
instance variable.
class Vehicle{
int speed=50;
}
class Bike3 extends Vehicle{
int speed=100;
void display(){
System.out.println(speed);//will print speed of Bike
}
Bike3 b=new Bike3();
b.display();
}
}
Output:100

//example of super keyword
class Vehicle{
int speed=50;
}
int speed=100;
void display(){
System.out.println(super.speed);//will print speed of Vehicle now
}
b.display();
}
}
Output:50

super is used to invoke parent class
constructor.
class Vehicle{
Vehicle(){System.out.println("Vehicle is created");}
}
Bike5(){
super();//will invoke parent class constructor
System.out.println("Bike is created");
}
}
}
Output:
Vehicle is created
Bike is created

Program in case super is not required
class Person{
void message(){System.out.println("welcome");}
}
class Student17 extends Person{
void display(){
message();//will invoke parent class message() method
}
Student17 s=new Student17();
s.display();
}
}
Output:welcome

super can be used to invoke parent
class method
class Person{
void message(){System.out.println("welcome");}
}
class Student16 extends Person{
void message(){System.out.println("welcome to java");}
void display(){
message();//will invoke current class message() method
super.message();//will invoke parent class message() method
}
Student16 s=new Student16();
s.display();
}
}
Output:
welcome to java
welcome

public class Car {
public void m1() {
System.out.println("car 1");
}
public void m2() {
}
public String toString() {
return "vroom";
}
}
public class Truck extends Car {
public void m1() {
System.out.println("truck 1");
}
}
What is the output from the following code?
Truck mycar = new Truck();
System.out.println(mycar);
mycar.m1();
mycar.m2();

public class Car {
public void m1() {
}
public void m2() {
}
return "vroom";
}
}
public class Truck extends Car {
public void m1() {
System.out.println("truck 1");
}
public void m2() {
super.m1();
}
return super.toString() +
super.toString();
}
}
Suppose the Truck code changes as shown above. What is the output now?
Truck mycar = new Truck();
System.out.println(mycar);
mycar.m1();
mycar.m2();

Inheritance1

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