Add classical decorator implementation (#43)

Author: mperor

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/Coffee.java

@@ -0,0 +1,10 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+public interface Coffee {
+
+    int getCost();
+
+    default String getDescription() {
+        return this.getClass().getSimpleName();
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/CoffeeDecorator.java

@@ -0,0 +1,22 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+public abstract class CoffeeDecorator implements Coffee {
+
+    protected final Coffee coffee;
+    protected final int cost;
+
+    protected CoffeeDecorator(Coffee coffee, int cost) {
+        this.coffee = coffee;
+        this.cost = cost;
+    }
+
+    @Override
+    public int getCost() {
+        return coffee.getCost() + cost;
+    }
+
+    @Override
+    public String getDescription() {
+        return "%s + %s".formatted(coffee.getDescription(), Coffee.super.getDescription());
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/NormalCoffee.java

@@ -0,0 +1,14 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+public class NormalCoffee implements Coffee {
+
+    @Override
+    public int getCost() {
+        return 100;
+    }
+
+    @Override
+    public String getDescription() {
+        return "Coffee";
+    }
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/WithChocolate.java

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+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+public class WithChocolate extends CoffeeDecorator {
+
+    public WithChocolate(Coffee coffee) {
+        super(coffee, 150);
+    }
+
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/WithMilk.java

@@ -0,0 +1,9 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+public class WithMilk extends CoffeeDecorator {
+
+    public WithMilk(Coffee coffee) {
+        super(coffee, 50);
+    }
+
+}

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/WithSugar.java

@@ -0,0 +1,9 @@
+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+public class WithSugar extends CoffeeDecorator {
+
+    public WithSugar(Coffee coffee) {
+        super(coffee, 30);
+    }
+
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/structural/decorator/classic/CoffeeDecoratorTest.java

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+package pl.mperor.lab.java.design.pattern.structural.decorator.classic;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.stream.Stream;
+
+public class CoffeeDecoratorTest {
+
+    @Test
+    public void shouldAllowToDynamicallyExtendCoffeeWithMilkChocolateOrSugar() {
+        NormalCoffee normal = new NormalCoffee();
+        Coffee robustCoffee = new WithChocolate(new WithMilk(new WithSugar(normal)));
+        Assertions.assertTrue(normal.getCost() < robustCoffee.getCost());
+        Assertions.assertTrue(Stream.of("WithChocolate", "WithSugar", "WithMilk")
+                .allMatch(robustCoffee.getDescription()::contains)
+        );
+    }
+
+}