上传文件至 'w4'

w4/Circle.java

@@ -0,0 +1,22 @@
+public class Circle extends Shape{
+    private double radius;
+    public Circle(double radius){
+        if (radius <= 0){
+            throw new IllegalArgumentException("半径必须大于0");
+        }
+        this.radius = radius;
+    }
+    @Override
+    public double getArea() {
+        return Math.PI * radius * radius;
+    }
+
+    @Override
+    public String getShapeName() {
+        return "圆形";
+    }
+
+    public double getRadius() {
+        return radius;
+    }
+}

w4/Main.java

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+//TIP 要<b>运行</b>代码，请按 <shortcut actionId="Run"/> 或
+// 点击装订区域中的 <icon src="AllIcons.Actions.Execute"/> 图标。
+void main() {
+  //TIP 当文本光标位于高亮显示的文本处时按 <shortcut actionId="ShowIntentionActions"/>
+  // 查看 IntelliJ IDEA 建议如何修正。
+  IO.println(String.format("Hello and welcome!"));
+
+  for (int i = 1; i <= 5; i++) {
+    //TIP 按 <shortcut actionId="Debug"/> 开始调试代码。我们已经设置了一个 <icon src="AllIcons.Debugger.Db_set_breakpoint"/> 断点
+    // 但您始终可以通过按 <shortcut actionId="ToggleLineBreakpoint"/> 添加更多断点。
+    IO.println("i = " + i);
+  }
+}

w4/Rectangle.java

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+public class Rectangle extends Shape{
+    private double length;
+    private double width;
+
+    public Rectangle(double length, double width) {
+        if (length <= 0 || width <= 0) {
+            throw new IllegalArgumentException("长和宽必须大于0");
+        }
+        this.length = length;
+        this.width = width;
+    }
+
+    @Override
+    public double getArea() {
+        return length * width;
+    }
+
+    @Override
+    public String getShapeName() {
+        return "长方形";
+    }
+
+    public double getLength() {
+        return length;
+    }
+
+    public double getWidth() {
+        return width;
+    }
+}

w4/Shape.java

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

w4/ShapeUtil.java

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+public class ShapeUtil {
+    public static void printArea(Shape shape) {
+        if (shape == null) {
+            System.out.println("错误：图形对象为空");
+            return;
+        }
+
+        System.out.println("图形类型：" + shape.getShapeName());
+        System.out.println("面积：" + shape.getArea());
+        System.out.println("------------------------");
+    }
+}