四舍五入保留两位小数--Java

import java.math.BigDecimal;
import java.text.DecimalFormat;
 import java.text.NumberFormat;
 public class format {
    double f = 111231.5585;
     public void m1() {
         BigDecimal bg = new BigDecimal(f);
         double f1 = bg.setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
         System.out.println(f1);
     }
     /**
      * DecimalFormat转换最简便
      */
     public void m2() {
        DecimalFormat df = new DecimalFormat("#.00");
         System.out.println(df.format(f));
     }
     /**
      * String.format打印最简便
      */
     public void m3() {
         System.out.println(String.format("%.2f", f));
     }
     public void m4() {
         NumberFormat nf = NumberFormat.getNumberInstance();
        nf.setMaximumFractionDigits(2);
         System.out.println(nf.format(f));
     }

     public static void main(String[] args) {
         format f = new format();
         f.m1();
        f.m2();
         f.m3();
        f.m4();
    }

 }