问题描述
我正在尝试编写近似PI值的代码。 我正在做的是:
这是我的代码:
import java.awt.Color;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
import java.util.Random;
public class Main extends Frame {
int width = 800;
ArrayList<Point> list = new ArrayList<Point>();
public void points(Graphics g) {
int numPoint = 10000000;
for (int i = 0; i < numPoint; i++) {
int min = 23;
int max = 23 + width;
Random rand = new Random();
int x = rand.nextInt(width);
int y = (int) (Math.random() * (max - min + 1) + min);
Point temp = new Point(x,y);
list.add(temp);
if (inCircle(temp)) {
g.setColor(Color.green);
} else {
g.setColor(Color.blue);
}
g.drawLine(x,y,x,y);
}
}
public void paint(Graphics g) {
g.fillRect(0,1000,1000);
int x = width / 2;
int y = width / 2 + 23;
int radius = width / 2;
g.setColor(Color.WHITE);
g.drawoval(x - radius,y - radius,radius * 2,radius * 2);
g.drawRect(0,23,width,width);
points(g);
calculatingPI();
}
public void calculatingPI() {
double inCircle = 0;
double inRect = list.size();
for (Point p : list) {
if (inCircle(p)) {
inCircle++;
}
}
double ratio = inRect / inCircle;
System.out.print("PI is approximated to: " + 4 / ratio + " ");
}
public boolean inCircle(Point p) {
Point center = new Point(width / 2,width / 2 + 23);
return center.distance(p) <= width / 2;
}
public static void main(String[] args) {
Frame frame = new Main();
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent we) {
System.exit(0);
}
});
// circle coordinates.
frame.setSize(800,1000);
frame.setVisible(true);
}
}
即使大多数情况下该数字约为1,13,也可以很好地工作。
问题是: I减小矩形和圆形的大小越多(不更改点数),PI越不准确。我不明白,为什么呢?我的代码有问题吗?
不是吗?面积最小,点越准确,PI越准确。为什么不是这种情况?
解决方法
您正在使用整数像素。这意味着您制作的“圆圈”越小,逼近真实圆圈的效果就越差。例如,这是一个3x3像素正方形内的圆:它看起来根本不是圆形。
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要获得更好的近似值,请使用double
浮点数而不是整数。使用Point2D.Double
代替Point
类:
ArrayList<Point2D.Double> list = new ArrayList<>();
要生成随机点:
double x = Math.random() * width;
double y = Math.random() * (max - min) + min;
Point2D.Double temp = new Point2D.Double(x,y);
请注意,在您拥有max-min+1
的地方,+ 1必须删除。
要测试点是否在圆内:
public boolean inCircle(Point2D.Double p) {
Point2D.Double center = new Point2D.Double(width / 2d,width / 2d + 23);
return center.distance(p) <= width / 2d;
}