by Dinesh Thakur Category: Classes

Method Overloading: When multiple methods in the same class with same name, having different functions or types of parameters, it is known as Method Overloading. When an overloaded method is invoked, it is the responsibility of the compiler to select the appropriate overloaded method based on the number of argument(s) passed and if the numbers of argument(s) are same then depending upon the type of argument(s) passed to the method. Thus, the key to method overloading is a method's parameter list. A method's return type is not enough to distinguish between two overloaded methods. If the compiler detects two methods declarations with the same name and parameter list but different return types then it will generate an error.

When you work with a Java class library, you often encounter classes that have numerous methods with the same name. We have already being using this aspect of the language implicitly when displaying text using a variety of println) method. For example

System.out.println("Hello Java");

System.out.println (59); //displays int

System.out.println(true); //displays boolean

System.out.println(31.37); //displays double

System.out.println(); //no parameter

Although all these methods have the same name (println) but take different parameter list. The first takes a String, the second takes a int, third takes a boolean, fourth takes a double and fifth takes no parameter at all. Thus, println ()method is overloaded.

Method overloading is useful when you want to create a collection of methods that perform closely related functions under different conditions. These conditions are typically embodied in the parameters passed to each version of the method.

In order to understand the concept of method overloading, let us consider an example of a method that is used to calculate sum of two numbers. The method definition of method sumlnt ( ) is given

void sumInt(int x,int y) {
   int z=x+y;
   System.out.println ("Sum = "+z);
}

The above method when used in the program will calculate the sum of two integer numbers. Now suppose the we also want to calculate the sum of 2 double numbers in the same program. To solve this problem, we need to make a new method with different name and double
type parameters. The method header of this new method sumDouble () is
void sumDouble(double,double);
This will not cause any problem as we have two methods to keep track off. Now suppose that. we also want to calculate the sum of two float, long , characters in the same program. To do this, we need to make different functions with different names and different type of parameters. So, the method header of all these methods are shown below.

void sumInt (int,int) ;
void sumFloat(float,float);
void sumLong (long, long) ;
void sumChar(char,char);
void sumDouble(double,double);

It is now necessary to remember five different method names that actually perform the same related operations of calculating sum of two numbers. Maintaining, using and understanding such methods in the program becomes complex for the programmer. A better solution to the above problem is to use the concept of method overloading which relieves the programmer from this complexity by providing the facility to give the same name for multiple methods that perform similar related operations provided each differs in the number or type of its parameters. The following program illustrates how the above problem can be solved using the concept of method overloading.

/*program that calculate sum of two numbers of different types using concept of method overloading */

class SumTwoNum
{
     void sum(int x, int y)
     {
        System.out.println("Sum of Two Integer Numbers : " + (x+y));
     }
     void sum(double x,double y)
     {
        System.out.println("Sum of Two Double Numbers : " + (x+y));
     }
     void sum(char x,char y)
     {
        System.out.println("Sum of Two Characters are : " + (x+y)); 
     }
}
  public class MethodOverloading
  {
     public static void main(String[] args)
     {
         SumTwoNum obj = new SumTwoNum();
         obj.sum(10,20);   //call sum method with int parameter
         obj.sum(7.52,8.14); //call sum method with double parameters
         obj.sum('A','B'); //call sum method with char parameters
     }
  }

Method Overloading in Java with Example

In the above program, three methods are defined and invoked which have the same name sum () but differ only in their parameter types (int, double and char). For each call of the method, the compiler chooses the appropriate method by comparing the types of the arguments in the call against the parameter list of each defined method. So when the statement obj.sum (7.52, 8.14); is executed, the compiler invokes the method which takes double type parameters, as seen in output.

The above example shows the concept of method overloading in which multiple methods with the same name and same number of parameters differ only in their data types. The compiler can also distinguish the multiple methods with same name by different number of parameters of the method. This can be illustrated with the help of following program.

Program to show the concept of method overloading to calculate area where same name methods differ in number of parameters?

/*program that calculate area of different shapes in which data types are same but difference in number of parameters using concept of method overloading */

class AreaShape {
   void area(int x) {
      System.out.println("Area of square is = " + (x*x));
   }
   void area(int x,int y) {
       System.out.println("Area. of rectangle is = " + (x*y))
   }
   void area(int x,int y,int z) {
      doub1e s=(x+y+z)/2;
      double triArea;
      triArea = Math.sqrt(s*(s-x)*(s-y)*(s-z));
      System.out.println("Area of triangle is = " + triArea);
   }
}
public class AreaOverload {
   public static void main(String[] args) {
      AreaShape obj = new AreaShape();
      obj.area(10); //Call area(int x)
      obj.area(5,6); //Call area(int x,int y)
      obj.area(4,5,6); //Call area(int x,int y,int z)
   }
}
Output : Area of square is = 100
Area of rectangle is = 30
Area of triangle is = 6.48074069840786

Explaination: The above program is used to calculate the area of the square, rectangle and triangle. For this, three methods are declared and called separately. Each method has the same name area but differs only in the number of parameters. When the statement obj.area (10) ; is executed, the compiler invokes the method which contains only one parameter for calculating area of square. Now on execution of the statement obj. area (5, 6); the method area () with two parameters is invoked for calculating the area of rectangle. Similarly, the next call invokes method with three parameters.

Advantages of Method Overloading

The advantages of method overloading are:

1. We need to remember single name instead of multiple names of the methods that perform similar type of operations. This helps in reducing the complexity of making large programs.

2. Overloaded methods that perform similar tasks can make complex programs more readable, understandable and easy to debug.

3. Maintainability of the program becomes easier.

Method overloading is a powerful tool for creating group of related methods that only differ in the type of data sent to it. However, if not used properly such as using methods with same name for different purposes can cause considerable confusion which leads to additional overhead in terms of maintainability.
For Example: Methods performing various arithmetic operations like addition, subtraction, multiplication, division should not be overloaded with same named functions as they perform different unrelated operations ..
If the methods differ only in the return type then they are not considered as overloaded methods and hence the compiler generates an error message. This is because it is not possible for the compiler to determine which version of the method to call.





About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.



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