我有一个作业准备交,在作业中我必须使用递归来绘制10层深的嵌套圆,在我为此敲了几个小时后我终于完成了。我唯一的问题是,我绘制的图像是 10 层深还是实际上 11 层?
这个问题来自于这样一个事实:我已经明确指出递归在经过 10 层时结束,但我确实告诉该方法绘制原始圆圈,然后它调用自身。这让我觉得它绘制了第一个级别,然后下降 10 个级别,总共 11 个级别。它创建的图像下降得如此之远,以至于我无法数出圆圈:/
如有任何澄清,我们将不胜感激,谢谢!
// import statements
import java.awt.*;
import javax.swing.*;
public class RecursiveCircles
{
public static void main(String[] args)
{
// create a new canvas
RCanvas myCanvas = new RCanvas();
// create JFrame
JFrame myJframe = new JFrame();
myJframe.setTitle("Recursive Circles");
// set JFrame size, location and close operation
myJframe.setSize(1500, 500);
myJframe.setLocation(100, 100);
myJframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// and canvas to JFrame and make it visble
myJframe.getContentPane().add(myCanvas);
myJframe.setVisible(true);
} // end main
} // end class RecursiveCircles
/*
* this class will draw the main circle of the image and will have the recursive
* method that draws the two outer circles down 10 levels
*/
class RCanvas extends Canvas
{
// defualt constructor
public RCanvas ()
{}
public void paint (Graphics graphics)
{
// declare variables
String title = "Recursive Circles";
int n = 300; // diamerter of the circle
int xOrigin = 600; // x location of start of circle (makes circle around the origin I wanted
int yOrigin = 100; // y location of start of circle (makes circle around the origin i wanted
int radius = n/2; // radius of circle (half the diamerter
int level = 10;
// make canvas background color black
graphics.setColor(Color.black); // make the background color black
graphics.fillRect(0, 0, 1500, 500); // rectangle that fills the JFrame
// put title on canvas
graphics.setColor(Color.BLUE);
graphics.drawString(title, 725, 50);
// draw main circle
graphics.setColor(Color.WHITE);
graphics.drawOval(xOrigin, yOrigin, n, n);
drawRCircles(graphics,xOrigin,yOrigin,radius,level); // call recrusrive method
System.out.println(level);
} // end paint
/*
* This is the recursive method that will draw the two circles on the outer sides of the
* main circle. it will then call itself and repate the process till it is 10 levels deep
*/
public void drawRCircles(Graphics graphics,int xOrigin,int yOrigin, int radius, int level)
{
int newRadius = (radius/2); // radius of smaller circle
int newXOrigin = xOrigin - (newRadius); // xOrigin of circle on left of the main circle
int newYOrigin = yOrigin + (newRadius); // yOrigin of circle on the right of the main circle
int newXOrigin2 = xOrigin + (newRadius*3); // xOrigin of circle on the right of the main circle
int newYOrigin2 = yOrigin + (newRadius); // yOrigin of circle on the right of the main circle
if (level > 0) // counts down from 10 to make the recursive image 10 levels deep
{
graphics.drawOval(newXOrigin, newYOrigin, newRadius*2, newRadius*2); // draw recursive circle on the left of main circle
graphics.drawOval(newXOrigin2, newYOrigin2, newRadius*2, newRadius*2); // draw recursive circle on the right of main circle
drawRCircles(graphics, newXOrigin, newYOrigin , newRadius, (level-1)); // make recursion of left circle
drawRCircles(graphics, newXOrigin2, newYOrigin2,newRadius,(level-1)); // make recursion of right circle
}// end if
} // end drawRCircles
}// end class
最佳答案
您的代码正在绘制 11 个圆圈,但您对 drawRCircles
本身的调用仅负责其中的 10 个。
更具体地说,这些线绘制了 1 个圆圈。
// draw main circle
graphics.setColor(Color.WHITE);
graphics.drawOval(xOrigin, yOrigin, n, n);
无论您是否有drawRCircles
函数,都会绘制这个圆。 (尝试删除它并运行您的代码,看看会发生什么。)
然后,您的代码调用 drawRCircles
函数 11 次,但自上次调用以来仅绘制 10 个圆圈,且 level = 0 测试失败 if(level > 0)
。
the Image it creates goes down so far that I can not count the circles :/
一个快速提示:因为您想知道,给定 N
的最大级别,它是否会绘制 N
或 N+1
级别对于圆圈,您也可以尝试将 level
变量更改为更易于管理的值(例如 2)并进行直观检查。
回到上面的代码,并忽略绘制主圆
部分(因为它独立于您的递归圆绘制)
drawRCircles(graphics,xOrigin,yOrigin,radius,level); // call recursive method
System.out.println(level);
并且在您的 public void drawRCircles(…)
函数中,
drawRCircles(…,level-1);
让我们用 level = 2 而不是 10 来检查它:
drawRCircles(…, 2)
--> Check if 1 > 0.
--> Yes, 1 > 0 so drawRCircles(…, 1)
--> Check if 0 > 0.
--> No, 0 = 0, so stop.
级别数 = 2 = 绘制的递归圆数。
关于java - 递归级别和循环计数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/21836814/