done windows example

Author: AdelDaniel

structural_design_pattern/decorator/window_example.dart

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+// Wikipedia First example (window/scrolling scenario)
+// The following example illustrates the use of decorators
+// using the window/scrolling scenario.
+// source https://en.wikipedia.org/wiki/Decorator_pattern#Java
+
+//step1
+// The Window interface class
+abstract class IWindow {
+  void draw(); // Draws the Window
+  String get getDescription; // returns a description of the Window
+}
+
+// step 2
+// Implementation of a simple Window without any scrollbars
+class SimpleWindow implements IWindow {
+  @override
+  void draw() => print("This is SimpleWindow Class Draw"); // Draw window
+
+  @override
+  String get getDescription => "simple window Description";
+}
+
+// step 3
+// The decorator interface class
+// abstract decorator class - note that it implements Window
+abstract class WindowDecorator implements IWindow {
+  final IWindow _windowToBeDecorated; // the Window being decorated
+
+  WindowDecorator(IWindow windowToBeDecorated)
+      : _windowToBeDecorated = windowToBeDecorated;
+
+  @override
+  void draw() => _windowToBeDecorated.draw(); //Delegation
+
+  @override
+  String get getDescription => _windowToBeDecorated.getDescription; //Delegation
+
+}
+
+// step 4
+// The following classes contain the decorators for all Window classes,
+// Step 4.1
+// The first concrete decorator which adds vertical scrollbar functionality
+class VerticalScrollBarDecorator extends WindowDecorator {
+  VerticalScrollBarDecorator(IWindow windowToBeDecorated)
+      : super(windowToBeDecorated);
+
+  @override
+  void draw() {
+    super.draw();
+    _drawVerticalScrollBar();
+  }
+
+  @override
+  String get getDescription =>
+      super.getDescription + ", including vertical scrollbars";
+
+  // new functionality >> Draw the vertical scrollbar
+  void _drawVerticalScrollBar() =>
+      print("add >> vertical scrollbar functionality");
+}
+
+// Step 4.2\
+// The second concrete decorator which adds horizontal scrollbar functionality
+class HorizontalScrollBarDecorator extends WindowDecorator {
+  HorizontalScrollBarDecorator(IWindow windowToBeDecorated)
+      : super(windowToBeDecorated);
+
+  @override
+  void draw() {
+    super.draw();
+    _drawHorizontalScrollBar();
+  }
+
+  @override
+  String get getDescription =>
+      super.getDescription + ", including horizontal scrollbars";
+
+  void _drawHorizontalScrollBar() =>
+      print("add >> horizontal scrollbar functionality");
+}
+
+// Here's a test program that creates a Window instance which is fully decorated
+//(i.e., with vertical and horizontal scrollbars),
+// and prints its description:
+void main(List<String> args) {
+  // Create a decorated Window with horizontal and vertical scrollbars
+  IWindow simpleWindowWithoutScrolling = SimpleWindow();
+  IWindow decoratedWindow = HorizontalScrollBarDecorator(
+      VerticalScrollBarDecorator(simpleWindowWithoutScrolling));
+
+  // Print the Window's description
+  print(decoratedWindow.getDescription);
+}
+
+// The output of this program is
+// "simple window Description, including vertical scrollbars, including horizontal scrollbars".
+
+// Notice how the getDescription method of the two decorators
+// first retrieve the decorated Window's description
+// and decorates it with a suffix.