Feat: Implement Payment System with Interfaces and Default Methodsfeat(task1): add payment system implementation

src/CardPayment.java

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+class CardPayment implements PaymentMethod {
+    @Override
+    public void pay(int amount) {
+        System.out.println("Pay card: " + amount + " грн");
+    }
+
+    @Override
+    public String name() {
+        return "Card";
+    }
+}

src/Main.java

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+//TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
+// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
+public class Main {
+    public static void main(String[] args) {
+            PaymentProcessor processor = new PaymentProcessor();
+            PaymentMethod card = new CardPayment();
+            PaymentMethod paypal = new PaypalPayment();
+            processor.process(card, 1000);
+            processor.process(paypal, 500);
+            System.out.println();
+            card.payWithFee(1000, 25);
+            paypal.payWithFee(500, 10);
+        }
+}
+
+

src/PaymentMethod.java

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+interface PaymentMethod {
+    String name();
+
+    void pay(int amount);
+
+    default void payWithFee(int amount, int fee) {
+        int totalAmount = amount + fee;
+        System.out.println("Total amount to pay: " + totalAmount);
+        pay(totalAmount);
+    }
+}
+
+
+

src/PaymentProcessor.java

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+class PaymentProcessor{
+    public void process(PaymentMethod method, int amount) {
+        System.out.println("Processing payment with " + method.name());
+        method.pay(amount);
+    }
+}

src/PaypalPayment.java

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+class PaypalPayment implements PaymentMethod {
+    @Override
+    public String name() {
+        return "PayPal";
+    }
+
+    @Override
+    public void pay(int amount) {
+        System.out.println("Paying " + amount + " using PayPal.");
+    }
+}