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Method Overloading is a feature that allows a class to have more than one method with the same name, if their argument lists are different. This is an important feature in java, there are several cases where we need more than one methods with same name, for example if we are building an application for calculator, we need different variants of add method based on the user inputs such as add(int, int), add(float, float) etc. It is similar to constructor overloading in Java, that allows a class to have more than one constructor with different argument lists. Argument list means the parameters that a method has: For example the argument list of a method add(int a, int b) having two int parameters is different from the argument list of the method add(int a, int b, int c) having three int parameters. Three ways to overload a methodIn order to overload a method, the argument lists of the methods must differ in either of these: 2. Data type of parameters. 3. Sequence of Data type of parameters. Invalid case of method overloading: 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 examplesAs discussed in the beginning of this guide, method overloading is done by declaring same method with different parameters. The parameters must be different in either of these: number, sequence or types of parameters (or arguments). Let’s see some examples of each of these cases.
Example 1: Overloading – Different Number of parameters in argument listThis example shows how method overloading is done by having different number of parameters. In this example, we have two methods with the same name but their parameters count is different. First disp() method has one parameter (char) while the second method disp() has two parameters (char, int). class DisplayOverloading { public void disp(char c) { System.out.println(c); } public void disp(char c, int num) { System.out.println(c + " "+num); } } class Sample { public static void main(String args[]) { DisplayOverloading obj = new DisplayOverloading(); obj.disp('a'); obj.disp('a',10); } }Output: a a 10Example 2: Overloading – Difference in data type of parametersIn this example, method disp() is overloaded based on the data type of parameters – We have two methods with the name disp() and number of parameters but the type of parameters is different. The first method has one char parameter while the second method has one int parameter. class DisplayOverloading2 { public void disp(char c) { System.out.println(c); } public void disp(int c) { System.out.println(c ); } } class Sample2 { public static void main(String args[]) { DisplayOverloading2 obj = new DisplayOverloading2(); obj.disp('a'); obj.disp(5); } }Output: Example3: Overloading – Sequence of data type of argumentsHere method disp() is overloaded based on sequence of data type of parameters – Both the methods have different sequence of data type in argument list. First method is having argument list as (char, int) and second is having (int, char). Since the sequence is different, the method can be overloaded without any issues. class DisplayOverloading3 { public void disp(char c, int num) { System.out.println("I’m the first definition of method disp"); } public void disp(int num, char c) { System.out.println("I’m the second definition of method disp" ); } } class Sample3 { public static void main(String args[]) { DisplayOverloading3 obj = new DisplayOverloading3(); obj.disp('x', 51 ); obj.disp(52, 'y'); } }Output: I’m the first definition of method disp I’m the second definition of method dispMethod Overloading and Type PromotionWhen 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. Lets take an example to see what I am talking here: class Demo{ void disp(int a, double b){ System.out.println("Method A"); } void disp(int a, double b, double c){ System.out.println("Method B"); } public static void main(String args[]){ Demo obj = new Demo(); /* I am passing float value as a second argument but * it got promoted to the type double, because there * wasn't any method having arg list as (int, float) */ obj.disp(100, 20.67f); } }Output: Method AAs you can see that I have passed the float value while calling the disp() method but it got promoted to the double type as there wasn’t any method with argument list as (int, float) But this type promotion doesn’t always happen, lets see another example: class Demo{ void disp(int a, double b){ System.out.println("Method A"); } void disp(int a, double b, double c){ System.out.println("Method B"); } void disp(int a, float b){ System.out.println("Method C"); } public static void main(String args[]){ Demo obj = new Demo(); /* This time promotion won't happen as there is * a method with arg list as (int, float) */ obj.disp(100, 20.67f); } }Output: As you see that this time type promotion didn’t happen because there was a method with matching argument type. 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 → double short → int → long → float → double int → long → float → double float → double long → float → double char → int → long → float → doubleThis can be represented as a diagram like this: Lets see few Valid/invalid cases of method overloadingCase 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: 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. Guess the answers before checking it at the end of programs: Answer: Question 2 – return type is different. Method name & argument list same. class Demo2 { public double myMethod(int num1, int num2) { System.out.println("First myMethod of class Demo"); return num1+num2; } public int myMethod(int var1, int var2) { System.out.println("Second myMethod of class Demo"); return var1-var2; } } class Sample5 { public static void main(String args[]) { Demo2 obj2= new Demo2(); obj2.myMethod(10,10); obj2.myMethod(20,12); } }Answer: |