Method overloading

• If a class has multiple methods having same
name but different in parameters, it is known
as Method Overloading.

• Suppose you have to perform addition of the
given numbers but there can be any number
of arguments, if you write the method such as
a( int, int) for two parameters, and b(int, int
,int) for three parameters then it may be
difficult for you as well as other programmers
to understand the behavior of the method
because its name differs.
• So, we perform method overloading to figure
out the program quickly.

Advantage of method overloading
• Method overloading increases the readability
of the program.

Different ways to overload the method
• By changing number of arguments
• By changing the data type

Method Overloading: changing no. of
arguments
class Adder
{
static int add(int a, int b)
{
return a+b;
}
static int add(int a, int b, int c)
{
return a+b+c;}
}

class TestOverloading1
{
public static void main(String[] args)
{
System.out.println(Adder.add(11,11));
System.out.println(Adder.add(11,11,11));
}
}

• we have created two methods, first add()
method performs addition of two numbers
and second add method performs addition of
three numbers.

Method Overloading: changing data
type of arguments
• class Adder
• {
• static int add(int a, int b)
• {return a+b;}
• static double add(double a, double b)
• {return a+b;}
• }

• class TestOverloading2
• {
• public static void main(String[] args)
• {
• System.out.println(Adder.add(11,11));
• System.out.println(Adder.add(12.3,12.6));
• }
• }

• we have created two methods that differs in
data type. The first add method receives two
integer arguments and second add method
receives two double arguments.

Why Method Overloading is not possible by
changing the return type of method only?
In java, method overloading is not possible by
changing the return type of the method only
because of ambiguity. Let's see how ambiguity
may occur:

• class Adder
• {
• static int add(int a,int b){return a+b;}
• static double add(int a,int b){return a+b;}
• }
• class TestOverloading3{
• public static void main(String[] args){
• System.out.println(Adder.add(11,11));//ambig
uity
• }}

Compile Time Error: method add(int, int) is
already defined in class Adder
System.out.println(Adder.add(11,11)); //Here,
how can java determine which sum() method
should be called?

Can we overload java main() method?

• Yes, by method overloading. You can have any
number of main methods in a class by method
overloading. But JVM calls main() method
which receives string array as arguments only.
Let's see the simple example:

class TestOverloading4
{
public static void main(String[] args)
{System.out.println("main with String[]");}
public static void main(String args)
{System.out.println("main with String");}
public static void main()
{System.out.println("main without args");}
}

Method Overriding in Java
• If subclass (child class) has the same method
as declared in the parent class, it is known
as method overriding in java.
• In other words, If subclass provides the
specific implementation of the method that
has been provided by one of its parent class, it
is known as method overriding.

Usage of Java Method Overriding
• Method overriding is used to provide specific
implementation of a method that is already
provided by its super class.
• Method overriding is used for runtime
polymorphism

Rules for Java Method Overriding
• method must have same name as in the
parent class
• method must have same parameter as in the
parent class.
• must be IS-A relationship (inheritance).

Understanding the problem without
method overriding
• class Vehicle{
• void run(){System.out.println("Vehicle is runn
ing");} }
• class Bike extends Vehicle{
• public static void main(String args[]){
• Bike obj = new Bike();
• obj.run();
• } }

Example of method overriding
• class Vehicle{
• void run(){System.out.println("Vehicle is running");} }
• class Bike2 extends Vehicle{
• void run(){System.out.println("Bike is running safely");}
• public static void main(String args[]){
• Bike2 obj = new Bike2();
• obj.run();
• }

super keyword in java
• The super keyword in java is a reference
variable which is used to refer immediate
parent class object.

Usage of java 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 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.

• lass Animal{
• String color="white";
• }
• class Dog extends Animal{
• String color="black";
• void printColor(){
• System.out.println(color);//prints color of Dog
class
• System.out.println(super.color);//prints color
of Animal class
• } }

• class TestSuper1
• {
• public static void main(String args[])
• {
• Dog d=new Dog();
• d.printColor();
• }}

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 Animal{
• void eat(){System.out.println("eating...");}
• }
• void eat(){System.out.println("eating bread...");}
• void bark(){System.out.println("barking...");}
• void work(){
• super.eat();
• bark();
• } }

• {
• {
• d.work();
• }
• }

super is used to invoke parent class
constructor.
• class Animal{
• Animal(){System.out.println("animal is created");}
• }
• Dog(){
• super();
• System.out.println("dog is created");
• }
• }

• {
• {
• }
• }

Method overloading

Recommended

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Method overloading (20)

More from Lovely Professional University (20)

Recently uploaded (20)

Method overloading