added course decorator example

src/learn/simple_decorator/Component.java

@@ -0,0 +1,5 @@
+package learn.simple_decorator;
+
+public interface Component {
+    void operation();
+}

src/learn/simple_decorator/ConcreteComponent.java

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+package learn.simple_decorator;
+
+public class ConcreteComponent implements Component {
+    @Override
+    public void operation() {
+        System.out.println("Concrete operation");
+    }
+}

src/learn/simple_decorator/ConcreteDecoratorA.java

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+package learn.simple_decorator;
+
+public class ConcreteDecoratorA extends Decorator {
+    public ConcreteDecoratorA(Component component) {
+        super(component);
+    }
+
+    @Override
+    public void operation() {
+        System.out.println("I am adding some new responsibilities here.");
+        super.operation();
+    }
+}

src/learn/simple_decorator/ConcreteDecoratorB.java

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+package learn.simple_decorator;
+
+public class ConcreteDecoratorB extends Decorator {
+    public ConcreteDecoratorB(Component component) {
+        super(component);
+    }
+
+    @Override
+    public void operation() {
+        addedBehavior();
+        super.operation();
+    }
+
+    private void addedBehavior() {
+        System.out.println("I am adding some new behavior here.");
+    }
+}

src/learn/simple_decorator/Decorator.java

@@ -0,0 +1,14 @@
+package learn.simple_decorator;
+
+public abstract class Decorator implements Component {
+    private Component component;
+
+    public Decorator(Component component) {
+        this.component = component;
+    }
+
+    @Override
+    public void operation() {
+        component.operation();
+    }
+}

src/learn/simple_decorator/Main.java

@@ -0,0 +1,11 @@
+package learn.simple_decorator;
+
+public class Main {
+    public static void main(String[] args) {
+        Component component = new ConcreteComponent();
+        component = new ConcreteDecoratorB(component);
+        component = new ConcreteDecoratorA(component);
+
+        component.operation();
+    }
+}