四舍五入精确

package test;

import java.text.NumberFormat;

public class ChangeType {

 /**
  * @param args
  */
 public static String change(double db,int n){
  //double dbt = db;
//  int a = (int) Math.pow(10,n);
//  double dbt = Math.floor(db*a)/a;
  //int a = 2^3;
  
//  System.out.println(a);
  NumberFormat   ddf1=NumberFormat.getNumberInstance()   ;  
  ddf1.setMaximumFractionDigits(n);
  String dbt = ddf1.format(db);
  //double dbt = (double)s;
  return dbt;
 }
 public static void main(String[] args) {
  // TODO Auto-generated method stub
  String aa = ChangeType.change(56.263882212121, 3);
 
  System.out.println(aa);
 }

}