Added Java lab programs

OnlinePaymentSystem.java

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+import java.util.Scanner;
+
+// -------- BASE CLASS --------
+class Payment {
+
+    double amount;
+
+    Payment(double amount) {
+        this.amount = amount;
+    }
+
+    double processPayment() {
+        return amount;
+    }
+}
+
+// -------- SUB CLASS : CREDIT CARD --------
+class CreditCardPayment extends Payment {
+
+    CreditCardPayment(double amount) {
+        super(amount);
+    }
+
+    double processPayment() {
+        return amount + (amount * 0.02); // 2% service charge
+    }
+}
+
+// -------- SUB CLASS : UPI --------
+class UPIPayment extends Payment {
+
+    UPIPayment(double amount) {
+        super(amount);
+    }
+
+    double processPayment() {
+        return amount + 5; // Flat ₹5 charge
+    }
+}
+
+// -------- SUB CLASS : NET BANKING --------
+class NetBankingPayment extends Payment {
+
+    NetBankingPayment(double amount) {
+        super(amount);
+    }
+
+    double processPayment() {
+        return amount + (amount * 0.015); // 1.5% service charge
+    }
+}
+
+// -------- MAIN CLASS --------
+public class OnlinePaymentSystem {
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        System.out.print("Enter payment amount: ");
+        double amount = sc.nextDouble();
+
+        System.out.println("\nChoose Payment Method:");
+        System.out.println("1. Credit Card");
+        System.out.println("2. UPI");
+        System.out.println("3. Net Banking");
+        System.out.print("Enter choice: ");
+        int choice = sc.nextInt();
+
+        Payment payment; // Base class reference
+
+        switch (choice) {
+            case 1:
+                payment = new CreditCardPayment(amount);
+                break;
+            case 2:
+                payment = new UPIPayment(amount);
+                break;
+            case 3:
+                payment = new NetBankingPayment(amount);
+                break;
+            default:
+                System.out.println("Invalid choice");
+                sc.close();
+                return;
+        }
+
+        // Dynamic method dispatch
+        double finalAmount = payment.processPayment();
+
+        System.out.println("\nFinal Payable Amount: ₹" + finalAmount);
+
+        sc.close();
+    }
+}