上传文件至 'w4'

w4/Circle.java

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

w4/Rectangle.java

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

w4/Shape.java

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+public abstract class Shape {
+    public abstract double getArea();
+}

w4/ShapeTest.java

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+public class ShapeTest {
+    public static void main(String[] args) {
+        // 创建各个图形对象
+        Shape c = new Circle(5);
+        Shape r = new Rectangle(4,6);
+        Shape t = new Triangle(3,4);
+
+        //统一调用工具打印面积
+        System.out.print("圆形：");
+        ShapeUtil.printArea(c);
+
+        System.out.print("矩形：");
+        ShapeUtil.printArea(r);
+
+        System.out.print("三角形：");
+        ShapeUtil.printArea(t);
+    }
+}

w4/ShapeUtil.java

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+public class ShapeUtil {
+    public static void printArea(Shape shape){
+        System.out.println("图形面积：" + shape.getArea());
+    }
+}