update

dart_ex_1/basic_class.dart

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+/* --------------------------------------------- 100 -------------------------------------------- */
+
+import 'dart:io';
+
+// void main() {
+  
+//   print("please enter your age");
+//   String? _age = stdin.readLineSync();
+//   int age = int.parse(_age!);
+//   int turn100 = 100 - age;
+//   print("your age is $turn100");
+//   if (age%2 > 0) {
+//     print("your age is odd");
+//   }
+//   else if (age%2 == 0) {
+//     print("your age is even");
+//   } 
+// }
+
+abstract class Component {
+  final String id;
+  final double x;
+  final double y;
+  final String themeColor;
+  final bool isVisible;
+
+  // The base constructor sets the foundation
+  Component({
+    required this.id,
+    required this.x,
+    required this.y,
+    this.themeColor = 'blue', // Default value
+    this.isVisible = true,    // Default value
+  });
+
+  void render();
+}
+
+
+class Button extends Component {
+  final String label;
+  final double width;
+  final double height;
+
+  Button({
+    // --- Unique to Button ---
+    required this.label,
+    required this.width,
+    required this.height,
+
+    // --- Passed to Component via super. ---
+    required super.id,
+    required super.x,
+    required super.y,
+    super.themeColor,  // Doesn't require coz if user not define it defaults to parent's 'blue'. But if user provide value, use super to assign provided value to parent class variable. 
+    super.isVisible,  // Doesn't require coz if user not define, it defaults to parent's 'true'
+
+
+    // "assert" is a "sanity check" that runs before the class is even fully created. It ensures you can't accidentally create an invisible button with a width of -50. If the condition fails, the program crashes (in debug mode) with your custom error message.
+  }) : assert(width > 0 && height > 0, 'Dimensions must be positive'); 
+
+  @override
+  void render() {
+    print('Rendering Button "$label" at ($x, $y) with color $themeColor');
+  }
+}
+
+
+void main() {
+  final loginBtn = Button(
+    label: 'Login',
+    width: 200,
+    height: 50,
+    id: 'btn_001',
+    x: 100,
+    y: 500,
+    themeColor: 'green', // Overriding the default
+  );
+
+  loginBtn.render();
+}
+
+// ------------------------------------------------------------------
+
+
+
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+