发一下第二题吧，错了请指正 public class Pingfanggen { //求平方根 public static void main(String[] args) { Scanner s = new Scanner(System.in); int n =s.nextInt(); String aString = String.format("%.3f",kaifang(n)); System.out.println(aString); } public static double kaifang(int n) { Double a = 1.0; Double b = n+0.0; while(a<b) { Double c = (a+b)/2.0; if((c*c-b)/0.001<1) { return c; } if(c*c<b) { a=c; b=(n+0.0)/c; }else if(c*c>b) { b=c; a=(n+0.0)/c; } else { return a; } } return a; } }