Implement payment strategy classes for Bitcoin, Credit Card, and PayPal

strategy/src/main/java/org/patterns/BitcoinPayment.java

@@ -0,0 +1,20 @@
+package org.patterns;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class BitcoinPayment implements PaymentStrategy {
+
+    static Logger log = LoggerFactory.getLogger(BitcoinPayment.class);
+
+    private final String wallet;
+
+    public BitcoinPayment(String wallet) {
+        this.wallet = wallet;
+    }
+
+    public void pay(double amount) {
+        log.info("Paid ${} using Bitcoin wallet: {}", amount, wallet);
+    }
+
+}

strategy/src/main/java/org/patterns/CreditCardPayment.java

@@ -0,0 +1,20 @@
+package org.patterns;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class CreditCardPayment implements PaymentStrategy {
+
+    static Logger log = LoggerFactory.getLogger(CreditCardPayment.class);
+
+    private final String cardNumber;
+
+    public CreditCardPayment(String cardNumber) {
+        this.cardNumber = cardNumber;
+    }
+
+    public void pay(double amount) {
+        log.info("Paid ${} using Credit Card: {}", amount, cardNumber);
+    }
+
+}

strategy/src/main/java/org/patterns/PayPalPayment.java

@@ -0,0 +1,20 @@
+package org.patterns;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class PayPalPayment implements PaymentStrategy {
+
+    static Logger log = LoggerFactory.getLogger(PayPalPayment.class);
+
+    private final String email;
+
+    public PayPalPayment(String email) {
+        this.email = email;
+    }
+
+    public void pay(double amount) {
+        log.info("Paid ${} using PayPal account: {}", amount, email);
+    }
+
+}

strategy/src/main/java/org/patterns/PaymentContext.java

@@ -0,0 +1,18 @@
+package org.patterns;
+
+public class PaymentContext {
+
+    private PaymentStrategy strategy;
+
+    public void setPaymentStrategy(PaymentStrategy strategy) {
+        this.strategy = strategy;
+    }
+
+    public void checkout(double amount) {
+        if (strategy == null) {
+            throw new IllegalStateException("Payment strategy not set!");
+        }
+        strategy.pay(amount);
+    }
+
+}

strategy/src/main/java/org/patterns/PaymentStrategy.java

@@ -0,0 +1,7 @@
+package org.patterns;
+
+public interface PaymentStrategy {
+
+    void pay(double amount);
+
+}