Add standard strategy design pattern with test case

Author: mperor

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/CreditCardStrategy.java

@@ -0,0 +1,11 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+import java.time.LocalDate;
+
+record CreditCardStrategy(String name, String cardNumber, String cvv, LocalDate dateOfExpiry) implements PaymentStrategy {
+
+    @Override
+    public void pay(double amount) {
+        System.out.println(amount + " paid by 💳 credit card!");
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/Item.java

@@ -0,0 +1,21 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+record Item(String upcCode, String name, int priceInCents) {
+
+    public double price() {
+        return (double) priceInCents / 100;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (!(o instanceof Item item)) return false;
+
+        return upcCode.equals(item.upcCode);
+    }
+
+    @Override
+    public int hashCode() {
+        return upcCode.hashCode();
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/PaymentStrategy.java

@@ -0,0 +1,6 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+public interface PaymentStrategy {
+
+    void pay(double amount);
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/PaypalStrategy.java

@@ -0,0 +1,9 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+public record PaypalStrategy(String emailId, String password) implements PaymentStrategy {
+
+    @Override
+    public void pay(double amount) {
+        System.out.println(amount + " paid with 📱 paypal!");
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/Shopping.java

@@ -0,0 +1,23 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+class Shopping {
+
+    private PaymentStrategy strategy;
+
+    Shopping(PaymentStrategy strategy) {
+        this.strategy = strategy;
+    }
+
+    void setStrategy(PaymentStrategy strategy) {
+        this.strategy = strategy;
+    }
+
+    void pay(ShoppingCart cart) {
+        pay(cart, strategy);
+    }
+
+    void pay(ShoppingCart cart, PaymentStrategy strategy) {
+        double total = cart.computeTotal();
+        strategy.pay(total);
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/ShoppingCart.java

@@ -0,0 +1,25 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+
+class ShoppingCart {
+
+    private final Map<Item, Integer> itemQuantities = new LinkedHashMap<>();
+
+    void addItem(Item item) {
+        addItem(item, 1);
+    }
+
+    void addItem(Item item, int quantities) {
+        assert quantities >= 1;
+        itemQuantities.merge(item, quantities, Integer::sum);
+    }
+
+    double computeTotal() {
+        return itemQuantities.entrySet()
+                .stream()
+                .mapToDouble(entry -> entry.getKey().price() * entry.getValue())
+                .sum();
+    }
+}

…ttern/behavioral/strategy/MathUtils.java …oral/strategy/lightweight/MathUtils.javaDesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/MathUtils.java renamed to DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/lightweight/MathUtils.java DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/MathUtils.java renamed to DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/lightweight/MathUtils.java

@@ -1,26 +1,26 @@
-package pl.mperor.lab.java.design.pattern.behavioral.strategy;
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.lightweight;
 
 import java.util.List;
 import java.util.function.Predicate;
 
-public class MathUtils {
+class MathUtils {
 
-    public static int totalValue(List<Integer> values) {
+    static int totalValue(List<Integer> values) {
         return totalValue(values, _ -> true);
     }
 
-    public static int totalValue(List<Integer> values, Predicate<Integer> selector) {
+    static int totalValue(List<Integer> values, Predicate<Integer> selector) {
         return values.stream()
                 .filter(selector)
                 .mapToInt(e -> e)
                 .sum();
     }
 
-    public static boolean isEven(int number) {
+    static boolean isEven(int number) {
         return number % 2 == 0;
     }
 
-    public static boolean isOdd(int number) {
+    static boolean isOdd(int number) {
         return !isEven(number);
     }
 }

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/classic/PaymentStrategyTest.java

@@ -0,0 +1,41 @@
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.classic;
+
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import pl.mperor.lab.common.TestUtils;
+
+import java.time.LocalDate;
+
+public class PaymentStrategyTest {
+
+    @Test
+    public void shouldShoppingAllowToPayWithDifferentPaymentStrategy() {
+        Shopping shopping = new Shopping(new PaypalStrategy("mypaypall@example.com", "1234"));
+        ShoppingCart shoppingCart = new ShoppingCart();
+        shoppingCart.addItem(new Item("b1", "Smart TV", 999_00));
+        shoppingCart.addItem(new Item("b2", "Raspberry Pi", 99_99));
+        shoppingCart.addItem(new Item("b3", "DVD Player", 44_95));
+
+        var out = TestUtils.setTempSystemOut();
+        shopping.pay(shoppingCart);
+        shopping.setStrategy(new CreditCardStrategy("John Doe", "1234 1111 2222 1010", "123", LocalDate.parse("2025-12-31")));
+        shopping.pay(shoppingCart);
+        shopping.pay(shoppingCart, _ -> System.out.println("Fake payment 💰, do not use in production!"));
+
+        var outLines = out.lines();
+        Assertions.assertTrue(outLines.getFirst().endsWith("paid with 📱 paypal!"));
+        Assertions.assertTrue(outLines.getSecond().endsWith("paid by 💳 credit card!"));
+        Assertions.assertEquals("Fake payment 💰, do not use in production!", outLines.getThird());
+        TestUtils.resetSystemOut();
+    }
+
+    @Test
+    public void shouldReturnCorrectTotalPriceWhenItemsAdded() {
+        var cart = new ShoppingCart();
+        cart.addItem(new Item("A1", "iPhone X", 2000 * 100));
+        cart.addItem(new Item("A2", "Laptop", 2500 * 100), 2);
+        cart.addItem(new Item("A3", "Tablet Neo", 199 * 100), 3);
+        Assertions.assertEquals(7597d, cart.computeTotal());
+    }
+}

…al/strategy/LightweightStrategyTest.java …gy/lightweight/SelectorStrategyTest.javaDesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/LightweightStrategyTest.java renamed to DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/lightweight/SelectorStrategyTest.java DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/LightweightStrategyTest.java renamed to DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/strategy/lightweight/SelectorStrategyTest.java

@@ -1,14 +1,14 @@
-package pl.mperor.lab.java.design.pattern.behavioral.strategy;
+package pl.mperor.lab.java.design.pattern.behavioral.strategy.lightweight;
 
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
 import java.util.List;
 
-public class LightweightStrategyTest {
+public class SelectorStrategyTest {
 
     @Test
-    public void testTotalValueStrategy() {
+    public void testMathUtilsWithSelectorStrategy() {
         var values = List.of(1, 2, 3, 4);
         Assertions.assertEquals(10, MathUtils.totalValue(values));
         Assertions.assertEquals(6, MathUtils.totalValue(values, MathUtils::isEven));