Theory
Method Overloading is a feature that allows a class to have more than one method having the same name, if their argument lists are different. It is similar to constructor overloading in Java, that allows a class to have more than one constructor having different argument lists. Let’s get back to the point, when I say argument list it means the parameters that a method has: For example the argument list of a method add(int a, int b) having two parameters is different from the argument list of the method add(int a, int b, int c) having three parameters.
Three ways to overload a method
In order to overload a method, the argument lists of the methods must differ in either of these:
1. Number of parameters:
For example: This is a valid case of overloading
add(int, int)
add(int, int, int)
2. Data type of parameters
For example:
add(int, int)
add(int, float)
3. Sequence of Data type of parameters.
For example:
add(int, float)
add(float, int)
Invalid case of method overloading:
When I say argument list, I am not talking about return type of the method, for example if two methods have same name, same parameters and have different return type, then this is not a valid method overloading example. This will throw compilation error.
int add(int, int)
float add(int, int)
Method overloading is an example of Static Polymorphism. We will discuss polymorphism and types of it in a separate tutorial.
Points to Note:
1. Static Polymorphism is also known as compile time binding or early binding.
2. Static binding happens at compile time. Method overloading is an example of static binding where binding of method call to its definition happens at Compile time.
Method Overloading and Type Promotion
When a data type of smaller size is promoted to the data type of bigger size than this is called type promotion, for example: byte data type can be promoted to short, a short data type can be promoted to int, long, double etc.
What it has to do with method overloading?
Well, it is very important to understand type promotion else you will think that the program will throw compilation error but in fact that program will run fine because of type promotion.
Type Promotion table:
The data type on the left side can be promoted to the any of the data type present in the right side of it.
byte → short → int → long
short → int → long
int → long → float → double
float → double
long → float → double
Lets see few Valid/invalid cases of method overloading:
Case 1:
int mymethod(int a, int b, float c)
int mymethod(int var1, int var2, float var3)
Result: Compile time error. Argument lists are exactly same. Both methods are having same number, data types and same sequence of data types.
Case 2:
int mymethod(int a, int b)
int mymethod(float var1, float var2)
Result: Perfectly fine. Valid case of overloading. Here data types of arguments are different.
Case 3:
int mymethod(int a, int b)
int mymethod(int num)
Result: Perfectly fine. Valid case of overloading. Here number of arguments are different.
Case 4:
float mymethod(int a, float b)
float mymethod(float var1, int var2)
Result: Perfectly fine. Valid case of overloading. Sequence of the data types of parameters are different, first method is having (int, float) and second is having (float, int).
Case 5:
int mymethod(int a, int b)
float mymethod(int var1, int var2)
Result: Compile time error. Argument lists are exactly same. Even though return type of methods are different, it is not a valid case. Since return type of method doesn’t matter while overloading a method.