Day 7: polymorphism method overloading

What is method overloading?

Method Overloading is when a class has multiple methods with the same name but different parameters (different type, number, or order of parameters).

Why:

To increase code readability and reusability by performing similar operations with different inputs.
When is Method Overloading used?

when:

When we need to perform similar operations with different types or numbers of inputs.

Example:
In a calculator class:

add(int a, int b)  
add(double a, double b)  
add(int a, int b, int c)

All methods are named add but work with different arguments.

Which methods can be overloaded?#$

Any instance or static method can be overloaded, but constructors can also be overloaded.
Method overloading is not based on return type — only the method signature (name + parameters).

Real-Time Java Program: ATM Balance Checker (Method Overloading)

class ATM {
    // Method 1: Check balance using account number
    void checkBalance(int accountNumber) {
        System.out.println("Welcome to the ATM.");
        System.out.println("Account Number: " + accountNumber);
        System.out.println("Balance: ₹25,000");
        System.out.println("----------------------------------");
    }

    // Method 2: Check balance using account number and PIN
    void checkBalance(int accountNumber, int pin) {
        if (pin == 1234) {
            System.out.println("Authentication Successful!");
            System.out.println("Account Number: " + accountNumber);
            System.out.println("Balance: ₹25,000");
        } else {
            System.out.println("Invalid PIN. Please try again.");
        }
        System.out.println("----------------------------------");
    }

    // Method 3: Check balance using card number
    void checkBalance(String cardNumber) {
        System.out.println("Card Number: " + cardNumber);
        System.out.println("Balance: ₹25,000");
        System.out.println("----------------------------------");
    }
}

public class BankSystem {
    public static void main(String[] args) {
        ATM atm = new ATM();

        // Using account number only
        atm.checkBalance(100112233);

        // Using account number and correct PIN
        atm.checkBalance(100112233, 1234);

        // Using account number and wrong PIN
        atm.checkBalance(100112233, 1111);

        // Using card number
        atm.checkBalance("CARD456789123");
    }
}

Output:

Welcome to the ATM.
Account Number: 100112233
Balance: ₹25,000
----------------------------------
Authentication Successful!
Account Number: 100112233
Balance: ₹25,000
----------------------------------
Invalid PIN. Please try again.
----------------------------------
Card Number: CARD456789123
Balance: ₹25,000
----------------------------------

This real-time simulation shows how the same method name checkBalance() behaves differently based on the input. This is a practical use of Method Overloading.