题目：*18.19 (思瑞平斯基三角形)
修改程序清单18-9, 开发一个程序让用户使用 “+” 和 "-” 按钮将当前阶数增1或减1，如图 18 -12a 所示。初始阶数为0。如果当前阶数为0，就忽略按钮。
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代码示例
编程练习题18_19SierpinskiTriangle.java
package chapter_18;import javafx.application.Application;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Line;
import javafx.stage.Stage;public class 编程练习题18_19SierpinskiTriangle extends Application{private static int order = 0;@Overridepublic void start(Stage primaryStage) throws Exception {SierpinskiTrianglePane trianglePane = new SierpinskiTrianglePane();Button btAdd = new Button("+");btAdd.setOnMouseClicked(e ->{trianglePane.increaseByOne();});Button btSubtract = new Button("-");btSubtract.setOnMouseClicked(e ->{trianglePane.decreaseByOne();});HBox hBox = new HBox(10);hBox.getChildren().addAll(btAdd,btSubtract);hBox.setAlignment(Pos.CENTER);BorderPane borderPane = new BorderPane();borderPane.setCenter(trianglePane);borderPane.setBottom(hBox);Scene scene = new Scene(borderPane, 200, 210);primaryStage.setTitle("编程练习题18_19SierpinskiTriangle");primaryStage.setScene(scene);primaryStage.show();}static class SierpinskiTrianglePane extends Pane{private int order = 0;public void setOrder(int order) {this.order = order;paint();}SierpinskiTrianglePane(){}protected void paint() {Point2D p1 = new Point2D(getWidth()/2, 10);Point2D p2 = new Point2D(10, getHeight() - 10);Point2D p3 = new Point2D(getWidth()-10, getHeight() -10);this.getChildren().clear();displayTriangles(order,p1,p2,p3);}private void displayTriangles(int order,Point2D p1,Point2D p2,Point2D p3) {if(order < 0) {System.out.println("Order must be non-negative");return;}if(order == 0){/*Polygon triangle = new Polygon();triangle.getPoints().addAll(p1.getX(),p1.getY(),p2.getX(),p2.getY(),p3.getX(),p3.getY());triangle.setStroke(Color.BLACK);triangle.setFill(Color.WHITE);this.getChildren().add(triangle);*/Line l1 = new Line(p1.getX(), p1.getY(), p2.getX(), p2.getY()); Line l2 = new Line(p2.getX(), p2.getY(), p3.getX(), p3.getY()); Line l3 = new Line(p3.getX(), p3.getY(), p1.getX(), p1.getY()); this.getChildren().addAll(l1,l2,l3);}else {Point2D p12 = p1.midpoint(p2);Point2D p23 = p2.midpoint(p3);Point2D p31 = p3.midpoint(p1);displayTriangles(order-1, p1, p12, p31);displayTriangles(order-1, p12, p2, p23);displayTriangles(order-1, p31, p23, p3);}}public void decreaseByOne() {if (order > 0) {setOrder(order - 1);}}public void increaseByOne() {setOrder(order + 1);}}public static void main(String[] args) {Application.launch(args);}
}
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结果展示
