上传文件至 'w4'

w4/Circle.java

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+package shiyan2;
+
+public class Circle extends Shape {
+    private double radius;
+
+    public Circle(double radius) {
+        this.radius = radius;
+    }
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+}

w4/Rectangle.java

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+package shiyan2;
+
+public class Rectangle extends Shape {
+    private double width, height;
+    public Rectangle(double width, double height) {
+        this.width = width;
+        this.height = height;
+    }
+    public double getArea() {return width*height;}
+}

w4/Shape.java

@@ -0,0 +1,7 @@
+package shiyan2;
+
+
+public abstract class Shape {
+    public abstract double getArea();
+}
+

w4/ShapeUtil.java

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+package shiyan2;
+
+// ShapeUtil.java
+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        System.out.println("图形的面积为：" + shape.getArea());
+    }
+}

w4/Test.java

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+package shiyan2;
+
+// Test.java
+public class Test {
+    public static void main(String[] args) {
+        Shape circle = new Circle(3);
+        Shape rectangle = new Rectangle(4, 5);
+        Shape triangle = new Triangle(6, 7);
+
+        ShapeUtil.printArea(circle);
+        ShapeUtil.printArea(rectangle);
+        ShapeUtil.printArea(triangle);
+    }
+}