Super and final in java

PRESENTED BY:
ANSHU SHARMA
Object Oriented Using Java -
Super and Final Keyword

SUPER KEYWORD IN JAVA
 The super keyword in Java is a reference variable
which is used to refer immediate parent class object.
 Whenever you create the instance of subclass, an
instance of parent class is created implicitly which is
referred by super reference variable.
 It is used to call superclass methods, and to access
the superclass constructor.
 The most common use of the super keyword is to
eliminate the confusion between superclasses and
subclasses that have methods with the same name.

USE OF SUPER KEYWORD
 super can be used to refer immediate parent class instance
variable.
 super can be used to invoke immediate parent class
method.
 super() can be used to invoke immediate parent class
constructor.
 super () calls the parent class constructor with no
argument.
 super.methodname calls method from parents class.
 It is used to call the parents class variable.

EXAMPLES: 1) SUPER IS USED TO REFER
IMMEDIATE PARENT CLASS INSTANCE VARIABLE.
 We can use super keyword to access the data member or field of
parent class. It is used if parent class and child class have same
fields.
class vehicle{
String color="white";
}
class car extends vehicle{
String color="black";
void printColor(){
System.out.println(color);//prints color of car class
System.out.println(super.color);//prints color of vehicle class
}
}

EXAMPLE CONTD.
class TestSuper1{
public static void main(String args[]){
car c=new car();
c.printColor();
In the above example, vehicle and car both classes
have a common property color. If we print color
property, it will print the color of current class by
default. To access the parent property, we need to
use super keyword.

2) SUPER CAN BE USED TO
INVOKE PARENT CLASS METHOD
 The super keyword can also be used to invoke parent class
method. It should be used if subclass contains the same method
as parent class. In other words, it is used if method is overridden.
class person{
void eat(){System.out.println("eating...");}
}
class student extends person{
void eat(){System.out.println("eating ...");}
void read(){System.out.println(“Reading...");}
void work(){
super.eat();
read();
}
}

EXAMPLE CONTD.
class TestSuper2{
student d=new student();
d.work();
}}
In the above example person and student both classes
have eat() method if we call eat() method from
student class, it will call the eat() method of student
class by default because priority is given to local.

3) SUPER IS USED TO INVOKE
PARENT CLASS CONSTRUCTOR.
 The super keyword can also be used to invoke the parent class
constructor. Let's see a simple example:
class person{
person()
{
System.out.println(“person class");}
}
class student extends person{
student()
{
super();
System.out.println(“student class");
}
}

EXAMPLE CONTD.
class TestSuper3{
student d=new student();
}}
Output:
person class
Student class
As we know well that default constructor is provided by compiler
automatically if there is no constructor. But, it also adds super() as the
first statement.

FINAL KEYWORD IN JAVA
 The final keyword in java is used to restrict the user. The
java final keyword can be used in many context. Final can
be:
• A variable
• A method
• A class
 The final keyword can be applied with the variables, a final
variable that have no value it is called blank final variable or
uninitialized final variable. It can be initialized in the
constructor only. The blank final variable can be static also
which will be initialized in the static block only.

1) JAVA FINAL VARIABLE
 If you make any variable as final, you cannot
change the value of final variable(It will be
constant).
Example of final variable
 There is a final variable speedlimit, we are going to
change the value of this variable, but It can't be
changed because final variable once assigned a
value can never be changed.

EXAMPLE:
class Bike9{
final int speedlimit=90;//final variable
void run(){
speedlimit=400;
}
Bike9 obj=new Bike9();
obj.run();
}
}//end of class
Output:
Compile Time Error

2) JAVA FINAL METHOD
 If you make any method as final, you cannot override it.
Example of final method
class Bike{
final void run()
{
System.out.println("running");}
}
class Honda extends Bike{
void run()
{
System.out.println("running safely with 100kmph");
}

EXAMPLE CONTD.
public static void main(String args[])
{
Honda honda= new Honda();
honda.run();
}
}
Output:
Compile Time Error

3) JAVA FINAL CLASS
If you make any class as final, you cannot extend it.
Example of final class
final class Bike{}
class Honda1 extends Bike{
void run(){System.out.println("running safely with 100kmph");}
Honda1 honda= new Honda1();
honda.run();
}
}
Output:
Compile Time Error

Super and final in java

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