将w4文件夹及五个文件上传

w4/Circle.java

@@ -0,0 +1,23 @@
+package w4;
+
+public class Circle extends Shape {
+    private double radius; 
+    public Circle() {}
+
+    public Circle(double radius) {
+        this.radius = radius;
+    }
+
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+
+    public double getRadius() {
+        return radius;
+    }
+
+    public void setRadius(double radius) {
+        this.radius = radius;
+    }
+}

w4/Rectangle.java

@@ -0,0 +1,34 @@
+package w4;
+
+public class Rectangle extends Shape {
+    private double length; 
+    private double width;  
+
+    public Rectangle() {}
+
+    public Rectangle(double length, double width) {
+        this.length = length;
+        this.width = width;
+    }
+
+    @Override
+    public double getArea() {
+        return length * width;
+    }
+
+    public double getLength() {
+        return length;
+    }
+
+    public void setLength(double length) {
+        this.length = length;
+    }
+
+    public double getWidth() {
+        return width;
+    }
+
+    public void setWidth(double width) {
+        this.width = width;
+    }
+}

w4/Shape.java

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+package w4;
+
+public abstract class Shape {
+
+    public abstract double getArea();
+}

w4/ShapeUtil.java

@@ -0,0 +1,18 @@
+package w4;
+
+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        System.out.println("该图形的面积为：" + shape.getArea());
+    }
+
+    public static void main(String[] args) {
+        Shape circle = new Circle(5);
+        printArea(circle);
+
+        Shape rectangle = new Rectangle(4, 6);
+        printArea(rectangle);
+
+        Shape triangle = new Triangle(3, 8);
+        printArea(triangle);
+    }
+}

w4/Triangle.java

@@ -0,0 +1,34 @@
+package w4;
+
+public class Triangle extends Shape {
+    private double base;  
+    private double height; 
+
+    public Triangle() {}
+
+    public Triangle(double base, double height) {
+        this.base = base;
+        this.height = height;
+    }
+
+    @Override
+    public double getArea() {
+        return (base * height) / 2;
+    }
+
+    public double getBase() {
+        return base;
+    }
+
+    public void setBase(double base) {
+        this.base = base;
+    }
+
+    public double getHeight() {
+        return height;
+    }
+
+    public void setHeight(double height) {
+        this.height = height;
+    }
+}