If a class has multiple methods having same name but different in parameters, it is known as Method Overloading.
If we have to perform only one operation, having same name of the methods increases the readability of the program.
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

There are two ways to overload the method in java
1. By changing number of arguments
2. By changing the data type
In java, Method Overloading is not possible by changing the return type of the method only.

1) Method Overloading: changing no. of arguments

In this example, we have created two methods, first add() method performs addition of two numbers and second add method performs addition of three numbers.
In this example, we are creating static methods so that we don’t need to create instance for calling methods.

1. class Adder{
2. static int add(int a,int b){return a+b;}
3. static int add(int a,int b,int c){return a+b+c;}
4. }
5. class TestOverloading1{
6. public static void main(String[] args){
7. System.out.println(Adder.add(11,11));
8. System.out.println(Adder.add(11,11,11));
9. }
}

Output:
22
33

2) Method Overloading: changing data type of arguments

In this example, 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.

1. class Adder{
2. static int add(int a, int b){return a+b;}
3. static double add(double a, double b){return a+b;}
4. }
5. class TestOverloading2{
6. public static void main(String[] args){
7. System.out.println(Adder.add(11,11));
8. System.out.println(Adder.add(12.3,12.6));
9. }}

Output:
22
24.9

Q) 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:

1. class Adder{
2. static int add(int a,int b){return a+b;}
3. static double add(int a,int b){return a+b;}
4. }
5. class TestOverloading3{
6. public static void main(String[] args){
7. System.out.println(Adder.add(11,11));//ambiguity
8. }}

Output:
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?
Note: Compile Time Error is better than Run Time Error. So, java compiler renders compiler time error if you declare the same method having same parameters.

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:

1. class TestOverloading4{
2. public static void main(String[] args){System.out.println("main with String[]");}
3. public static void main(String args){System.out.println("main with String");}
4. public static void main(){System.out.println("main without args");}
5. }

Output:
main with String[]

Method Overloading and Type Promotion

One type is promoted to another implicitly if no matching datatype is found. Let’s understand the concept by the figure given below:

java 6

As displayed in the above diagram, byte can be promoted to short, int, long, float or double. The short datatype can be promoted to int, long, float or double. The char datatype can be promoted to int,long,float or double and so on.

Example of Method Overloading with TypePromotion

1. class OverloadingCalculation1{
2. void sum(int a,long b){System.out.println(a+b);}
3. void sum(int a,int b,int c){System.out.println(a+b+c);}
4.
5. public static void main(String args[]){
6. OverloadingCalculation1 obj=new OverloadingCalculation1();
7. obj.sum(20,20);//now second int literal will be promoted to long
8. obj.sum(20,20,20);
9.
10. }
11. }

Output:40
60

Example of Method Overloading with Type Promotion if matching found

If there are matching type arguments in the method, type promotion is not performed.
1. class OverloadingCalculation2{
2. void sum(int a,int b){System.out.println("int arg method invoked");}
3. void sum(long a,long b){System.out.println("long arg method invoked");}
4.
5. public static void main(String args[]){
6. OverloadingCalculation2 obj=new OverloadingCalculation2();
7. obj.sum(20,20);//now int arg sum() method gets invoked
8. }
9. }

Output:intarg method invoked

Example of Method Overloading with Type Promotion in case of ambiguity

If there are no matching type arguments in the method, and each method promotes similar number of arguments, there will be ambiguity.
1. class OverloadingCalculation3{
2. void sum(int a,long b){System.out.println("a method invoked");}
3. void sum(long a,int b){System.out.println("b method invoked");}
4.
5. public static void main(String args[]){
6. OverloadingCalculation3 obj=new OverloadingCalculation3();
7. obj.sum(20,20);//now ambiguity
8. }
9. }

Output:Compile Time Error

One type is not de-promoted implicitly for example double cannot be depromoted to any type implicitly.

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 a subclass provides the specific implementation of the method that has been declared by one of its parent class, it is known as method overriding.
Usage of Java Method Overriding
• Method overriding is used to provide the specific implementation of a method which is already provided by its superclass.
• Method overriding is used for runtime polymorphism
Rules for Java Method Overriding
1. The method must have the same name as in the parent class
2. The method must have the same parameter as in the parent class.
3. There must be an IS-A relationship (inheritance).

java 7

Understanding the problem without method overriding

Let's understand the problem that we may face in the program if we don't use method overriding.
1. //Java Program to demonstrate why we need method overriding
2. //Here, we are calling the method of parent class with child
3. //class object.
4. //Creating a parent class
5. class Vehicle{
6. void run(){System.out.println("Vehicle is running");}
7. }
8. //Creating a child class
9. class Bike extends Vehicle{
10. public static void main(String args[]){
11. //creating an instance of child class
12. Bike obj = new Bike();
13. //calling the method with child class instance
14. obj.run();
15. }
16. }

Output:
Vehicle is running
Problem is that I have to provide a specific implementation of run() method in subclass that is why we use method overriding.

Example of method overriding

In this example, we have defined the run method in the subclass as defined in the parent class but it has some specific implementation. The name and parameter of the method are the same, and there is IS-A relationship between the classes, so there is method overriding.
1. //Java Program to illustrate the use of Java Method Overriding
2. //Creating a parent class.
3. class Vehicle{
4. //defining a method
5. void run(){System.out.println("Vehicle is running");}
6. }
7. //Creating a child class
8. class Bike2 extends Vehicle{
9. //defining the same method as in the parent class
10. void run(){System.out.println("Bike is running safely");}
11.
12. public static void main(String args[]){
13. Bike2 obj = new Bike2();//creating object
14. obj.run();//calling method
15. }
16. }
Output:
Bike is running safely

A real example of Java Method Overriding

Consider a scenario where Bank is a class that provides functionality to get the rate of interest. However, the rate of interest varies according to banks. For example, SBI, ICICI and AXIS banks could provide 8%, 7%, and 9% rate of interest.

java 8 4

Java method overriding is mostly used in Runtime Polymorphism which we will learn in next pages.
1. //Java Program to demonstrate the real scenario of Java Method Overriding
2. //where three classes are overriding the method of a parent class.
3. //Creating a parent class.
4. class Bank{
5. int getRateOfInterest(){return 0;}
6. }
7. //Creating child classes.
8. class SBI extends Bank{
9. int getRateOfInterest(){return 8;}
10. }
11.
12. class ICICI extends Bank{
13. int getRateOfInterest(){return 7;}
14. }
15. class AXIS extends Bank{
16. int getRateOfInterest(){return 9;}
17. }
18. //Test class to create objects and call the methods
19. class Test2{
20. public static void main(String args[]){
21. SBI s=new SBI();
22. ICICI i=new ICICI();
23. AXIS a=new AXIS();
24. System.out.println("SBI Rate of Interest: "+s.getRateOfInterest());
25. System.out.println("ICICI Rate of Interest: "+i.getRateOfInterest());
26. System.out.println("AXIS Rate of Interest: "+a.getRateOfInterest());
27. }
28. }

Output:
SBI Rate of Interest: 8
ICICI Rate of Interest: 7
AXIS Rate of Interest: 9

Can we override static method?

No, a static method cannot be overridden. It can be proved by runtime polymorphism, so we will learn it later.

Why can we not override static method?

It is because the static method is bound with class whereas instance method is bound with an object. Static belongs to the class area, and an instance belongs to the heap area.

Can we override java main method?

No, because the main is a static method.
So, this brings us to the end of blog. This Tecklearn ‘Concept of Method Overloading and Method Overriding in Java’ blog helps you with commonly asked questions if you are looking out for a job in Java Programming. If you wish to learn Java and build a career Java Programming domain, then check out our interactive, Java and JEE Training, that comes with 24*7 support to guide you throughout your learning period. Please find the link for course details:

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