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。

• 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;
	@Override
	public 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);
	}
}

•  结果展示