w4

w4+/Circle.java

@@ -0,0 +1,12 @@
+class Circle extends Shape {
+    private double radius;
+
+    Circle(double radius) {
+        this.radius = radius;
+    }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+}

w4+/Main.java

@@ -0,0 +1,11 @@
+public class Main {
+    public static void main(String[] args) {
+        Shape circle = new Circle(5.0);
+        Shape rectangle = new Rectangle(4.0, 6.0);
+        Shape triangle = new Triangle(3.0, 8.0);
+
+        ShapeUtil.printArea(circle);
+        ShapeUtil.printArea(rectangle);
+        ShapeUtil.printArea(triangle);
+    }
+}

w4+/Rectangle.java

@@ -0,0 +1,14 @@
+class Rectangle extends Shape {
+    private double width;
+    private double height;
+
+    Rectangle(double width, double height) {
+        this.width = width;
+        this.height = height;
+    }
+
+    @Override
+    public double getArea() {
+        return width * height;
+    }
+}

w4+/Shape.java

@@ -0,0 +1,3 @@
+abstract class Shape {
+    public abstract double getArea();
+}

w4+/ShapeUtil.java

@@ -0,0 +1,5 @@
+class ShapeUtil {
+    public static void printArea(Shape shape) {
+        System.out.printf("%.2f%n", shape.getArea());
+    }
+}

w4+/Triangle.java

@@ -0,0 +1,14 @@
+class Triangle extends Shape {
+    private double base;
+    private double height;
+
+    Triangle(double base, double height) {
+        this.base = base;
+        this.height = height;
+    }
+
+    @Override
+    public double getArea() {
+        return 0.5 * base * height;
+    }
+}