Different ways of Method Overloading in Java

Prerequisite : Overloading
Java can distinguish the methods with different method signatures. i.e. the methods can have same name but with different parameters list (i.e. number of the parameters, order of the parameters, and data types of the parameters) within the same class.

Overloaded methods are differentiated based on the number and type of the parameters passed as an arguments to the methods.
You can not define more than one method with the same name, Order and the type of the arguments. It would be compiler error.
The compiler does not consider the return type while differentiating the overloaded method. But you cannot declare two methods with the same signature and different return type. It will throw a compile time error.
If both methods have same parameter types, but different return type, then it is not possible. (Java SE 8 Edition, §8.4.2)

Why do we need Method Overloading ??

If we need to do same kind of the operation with different ways i.e. for different inputs. In the example described below, we are doing the addition operation for different inputs. It is hard to find many different meaningful names for single action.

Different ways of doing overloading methods

Method overloading can be done by changing:

The number of parameters in two methods.
The data types of the parameters of methods.
The Order of the parameters of methods.

Method 1: By changing the number of parameters.

import java.io.*; 
   
class Addition{ 
       
    // adding two integer values. 
    public int add(int a, int b){ 
           
        int sum = a+b; 
        return sum; 
    } 
       
    // adding three integer values. 
    public int add(int a, int b, int c){ 
           
        int sum = a+b+c; 
        return sum; 
    } 
       
} 
   
class GFG { 
    public static void main (String[] args) { 
           
        Addition ob = new Addition(); 
           
        int sum1 = ob.add(1,2); 
        System.out.println("sum of the two integer value :" + sum1); 
        int sum2 = ob.add(1,2,3); 
        System.out.println("sum of the three integer value :" + sum2); 
           
    } 
} 

Output:

sum of the two integer value :3
sum of the three integer value :6

Method 2: By changing the Data types of the parameters

import java.io.*; 
   
class Addition{ 
       
    // adding three integer values. 
    public int add(int a, int b, int c){ 
           
        int sum = a+b+c; 
        return sum; 
    } 
       
    // adding three double values. 
    public double add(double a, double b, double c){ 
           
        double sum = a+b+c; 
        return sum; 
    } 
} 
   
class GFG { 
    public static void main (String[] args) { 
           
        Addition ob = new Addition(); 
          
        int sum2 = ob.add(1,2,3); 
        System.out.println("sum of the three integer value :" + sum2); 
        double sum3 = ob.add(1.0,2.0,3.0); 
        System.out.println("sum of the three double value :" + sum3); 
           
           
    } 
} 

Output:

sum of the three integer value :6
sum of the three double value :6.0

Method 3: By changing the Order of the parameters

import java.io.*; 
   
class Geek{ 
       
    public void geekIdentity(String name,  int id){ 
           
        System.out.println("geekName :"+ name +" "+"Id :"+ id); 
    } 
       
    public void geekIdentity(int id, String name){ 
           
        System.out.println("geekName :"+ name +" "+"Id :"+ id); 
    } 
} 
   
class GFG { 
    public static void main (String[] args) { 
           
        Geek geek = new Geek(); 
           
        geek.geekIdentity("Mohit", 1); 
        geek.geekIdentity("shubham", 2); 
           
    } 
} 

Output:

geekName :Mohit Id :1
geekName :shubham Id :2

What happens when method signature is same and the return type is different?

The compiler will give error as the return value alone is not sufficient for the compiler to figure out which function it has to call. More details:Java Language Specification: §8.4.2.

Only if both methods have different parameter types (so, they have different signature), then Method overloading is possible.

// Example to show error when method signature is same  
// and return type is different. 
import java.io.*; 
  
class Addition 
{ 
    // adding two integer value. 
    public int add(int a, int b) 
    { 
          
        int sum = a+b; 
        return sum; 
    } 
      
    // adding three integer value. 
    public double add(int a, int b) 
    { 
        double sum = a+b+0.0; 
        return sum; 
    } 
    
} 
  
class GFG  
{ 
    public static void main (String[] args)  
    { 
        Addition ob = new Addition(); 
          
        int sum1 = ob.add(1,2); 
        System.out.println("sum of the two integer value :" + sum1); 
          
        int sum2 = ob.add(1,2); 
        System.out.println("sum of the three integer value :" + sum2); 
          
    } 
} 

Output:

16: error: method add(int,int) is already defined in class Addition
    public double add(int a, int b)
                  ^
1 error

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