Method Overloading in Java

In Java, Method Overloading allows different methods to have the same name, but different signatures where the signature can differ by the number of input parameters or type of input parameters, or a mixture of both.

Method overloading in Java is also known as Compile-time Polymorphism, Static Polymorphism, or Early binding. In Method overloading compared to the parent argument, the child argument will get the highest priority.

Example of Method Overloading

Java

// Java program to demonstrate working of method
// overloading in Java

public class Sum {
    // Overloaded sum(). This sum takes two int parameters
    public int sum(int x, int y) { return (x + y); }

    // Overloaded sum(). This sum takes three int parameters
    public int sum(int x, int y, int z)
    {
        return (x + y + z);
    }

    // Overloaded sum(). This sum takes two double
    // parameters
    public double sum(double x, double y)
    {
        return (x + y);
    }

    // Driver code
    public static void main(String args[])
    {
        Sum s = new Sum();
        System.out.println(s.sum(10, 20));
        System.out.println(s.sum(10, 20, 30));
        System.out.println(s.sum(10.5, 20.5));
    }
}

Output

30
60
31.0

Different Ways of Method Overloading in Java

• Changing the Number of Parameters.
• Changing Data Types of the Arguments.
• Changing the Order of the Parameters of Methods

1. Changing the Number of Parameters

Method overloading can be achieved by changing the number of parameters while passing to different methods.

Below is the implementation of the above method:

Java

// Java Program to Illustrate Method Overloading
// By Changing the Number of Parameters

// Importing required classes
import java.io.*;

// Class 1
// Helper class
class Product {
    // Method 1
    // Multiplying two integer values
    public int multiply(int a, int b)
    {
        int prod = a * b;
        return prod;
    }

    // Method 2
    // Multiplying three integer values
    public int multiply(int a, int b, int c)
    {
        int prod = a * b * c;
        return prod;
    }
}

// Class 2
// Main class
class GFG {
    // Main driver method
    public static void main(String[] args)
    {
        // Creating object of above class inside main()
        // method
        Product ob = new Product();

        // Calling method to Multiply 2 numbers
        int prod1 = ob.multiply(1, 2);

        // Printing Product of 2 numbers
        System.out.println(
            "Product of the two integer value :" + prod1);

        // Calling method to multiply 3 numbers
        int prod2 = ob.multiply(1, 2, 3);

        // Printing product of 3 numbers
        System.out.println(
            "Product of the three integer value :" + prod2);
    }
}

Output

Product of the two integer value :2
Product of the three integer value :6

2. Changing Data Types of the Arguments

In many cases, methods can be considered Overloaded if they have the same name but have different parameter types, methods are considered to be overloaded.

Below is the implementation of the above method:

Java

// Java Program to Illustrate Method Overloading
// By Changing Data Types of the Parameters

// Importing required classes
import java.io.*;

// Class 1
// Helper class
class Product {
    // Multiplying three integer values
    public int Prod(int a, int b, int c)
    {
        int prod1 = a * b * c;
        return prod1;
    }

    // Multiplying three double values.
    public double Prod(double a, double b, double c)
    {
        double prod2 = a * b * c;
        return prod2;
    }
}

class GFG {
    public static void main(String[] args)
    {
        Product obj = new Product();

        int prod1 = obj.Prod(1, 2, 3);
        System.out.println(
            "Product of the three integer value :" + prod1);

        double prod2 = obj.Prod(1.0, 2.0, 3.0);
        System.out.println(
            "Product of the three double value :" + prod2);
    }
}

Output

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

3. Changing the Order of the Parameters of Methods

Method overloading can also be implemented by rearranging the parameters of two or more overloaded methods. For example, if the parameters of method 1 are (String name, int roll_no) and the other method is (int roll_no, String name) but both have the same name, then these 2 methods are considered to be overloaded with different sequences of parameters.

Below is the implementation of the above method:

Java

// Java Program to Illustrate Method Overloading
// By changing the Order of the Parameters

// Importing required classes
import java.io.*;

// Class 1
// Helper class
class Student {
    // Method 1
    public void StudentId(String name, int roll_no)
    {
        System.out.println("Name :" + name + " "
                           + "Roll-No :" + roll_no);
    }

    // Method 2
    public void StudentId(int roll_no, String name)
    {
        // Again printing name and id of person
        System.out.println("Roll-No :" + roll_no + " "
                           + "Name :" + name);
    }
}

// Class 2
// Main class
class GFG {
    // Main function
    public static void main(String[] args)
    {
        // Creating object of above class
        Student obj = new Student();

        // Passing name and id
        // Note: Reversing order
        obj.StudentId("Spyd3r", 1);
        obj.StudentId(2, "Kamlesh");
    }
}

Output

Name :Spyd3r Roll-No :1
Roll-No :2 Name :Kamlesh

What if the exact prototype does not match with arguments?

 Priority-wise, the compiler takes these steps:

• Type Conversion but to a higher type(in terms of range) in the same family.
• Type conversion to the next higher family(suppose if there is no long data type available for an int data type, then it will search for the float data type).

Let’s take an example to clarify the concept:

Java

// Demo Class
class Demo {
    public void show(int x)
    {
        System.out.println("In int" + x);
    }
    public void show(String s)
    {
        System.out.println("In String" + s);
    }
    public void show(byte b)
    {
        System.out.println("In byte" + b);
    }
}

class UseDemo {
    public static void main(String[] args)
    {
        byte a = 25;
        Demo obj = new Demo();

        // it will go to
        // byte argument
        obj.show(a);

        // String
        obj.show("hello");

        // Int
        obj.show(250);

        // Since char is
        // not available, so the datatype
        // higher than char in terms of
        // range is int.
        obj.show('A');

        // String
        obj.show("A");

        // since float datatype
        // is not available and so it's higher
        // datatype, so at this step their
        // will be an error.
        obj.show(7.5);
    }
}

Output

./UseDemo.java:46: error: no suitable method found for show(double)
        obj.show(7.5);
           ^
    method Demo.show(int) is not applicable
      (argument mismatch; possible lossy conversion from double to int)
    method Demo.show(String) is not applicable
      (argument mismatch; double cannot be converted to String)
    method Demo.show(byte) is not applicable
      (argument mismatch; possible lossy conversion from double to byte)
1 error

Advantages of Method Overloading 

• Method overloading improves the Readability and reusability of the program.
• Method overloading reduces the complexity of the program.
• Using method overloading, programmers can perform a task efficiently and effectively.
• Using method overloading, it is possible to access methods performing related functions with slightly different arguments and types.
• Objects of a class can also be initialized in different ways using the constructors.

Important Questions in Java

Q1. Can we overload static methods?

Answer:

The answer is ‘Yes’. We can have two or more static methods with the same name, but differences in input parameters. For example, consider the following Java program. To know more about this, refer to the article – Can we Overload or Override static methods in Java?

Q2. Can we overload methods that differ only by static keywords?

Answer:

We cannot overload two methods in Java if they differ only by static keyword (the number of parameters and types of parameters are the same). See the following Java program for example. Refer to this for details. 

Q3. Can we overload main() in Java?

Answer:

Like other static methods, we can overload main() in Java. 

Java

// Java program with overloaded main()
import java.io.*;

public class Test {
    // Normal main()
    public static void main(String[] args)
    {
        System.out.println("Hi Geek (from main)");
        Test.main("Geek");
    }

    // Overloaded main methods
    public static void main(String arg1)
    {
        System.out.println("Hi, " + arg1);
        Test.main("Dear Geek", "My Geek");
    }

    public static void main(String arg1, String arg2)
    {
        System.out.println("Hi, " + arg1 + ", " + arg2);
    }
}

Output

Hi Geek (from main)
Hi, Geek
Hi, Dear Geek, My Geek

Q4. Does Java support Operator Overloading?

Answer:

Unlike C++, Java doesn’t allow user-defined overloaded operators. Internally Java overloads operators, for example, + is overloaded for concatenation. 

Q5. Can we overload methods on return type?

Answer:

We cannot overload by return type. This behavior is the same in C++. Refer to this for details.

Java

/*package whatever //do not write package name here */

import java.io.*;

public class Main {
    public int foo() { return 10; }

    // compiler error: foo() is already defined
    public char foo() { return 'a'; }

    public static void main(String args[]) {}
}

Error

./Main.java:8: error: method foo() is already defined in class Main
public char foo() { return 'a'; }
           ^
1 error

However, Overloading methods on return type are possible in cases where the data type of the function being called is explicitly specified. Look at the examples below:

Java

// Java program to demonstrate the working of method
// overloading in static methods

import java.io.*;

public class Main {

    public static int foo(int a) { return 10; }
    public static char foo(int a, int b) { return 'a'; }

    public static void main(String args[])
    {
        System.out.println(foo(1));
        System.out.println(foo(1, 2));
    }
}

Output

10
a

Java

// Java program to demonstrate working of method
// overloading in methods
class A {
    public int foo(int a) { return 10; }

    public char foo(int a, int b) { return 'a'; }
}

public class Main {

    public static void main(String args[])
    {
        A a = new A();
        System.out.println(a.foo(1));
        System.out.println(a.foo(1, 2));
    }
}

Output

10
a

Q6. What is the difference between Overloading and Overriding?

Answer:

Overloading is about the same function having different signatures. Overriding is about the same function, and same signature but different classes connected through inheritance.

Overloading is an example of compiler time polymorphism and overriding is an example of run time polymorphism.