疯狂java 讲义第三章练习题---画圆

思路：1.一行一行的打印，没一行会打印两个*，确定靠左边的那个*后，再间隔(r-x)*2空格，打印第二个*。

2.第一个*的坐标对应的x(0<=x<=r),故第一个*的坐标(r-sqrt(r*r-(r-y)*(r-y)) ,y);

package chapter3;

public class PaintingCycle {

private static int r;

PaintingCycle(int r){
this.r=r;
}
private static void paint(){
int y = r*2;
int x = 0;
int c = 0;
int z = 2;
for(int j=y;j>=0;j-=z){
x=getX(r,y);
System.out.print(getSpace(x)+"*");
c=(r-x)*2;
System.out.println(getSpace(c)+"*");
y-=z;
}
}
private static int getX(int r,int y){
int x = y-r;
double t = Math.sqrt(r*r-x*x);
return (int)Math.round(r-t);
}
private static String getSpace(int c){
String s = "";
for(int i=0;i<c;i++)
s+= " ";
return s;
}

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
new PaintingCycle(10).paint();
}

}