import java.math.BigDecimal;
import java.text.DecimalFormat;
import java.text.NumberFormat;

publicclass format {
    double f = 111231.5585;
    publicvoid 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
     */
    publicvoid m2() {
        DecimalFormat df = new DecimalFormat("#.00");
        System.out.println(df.format(f));
    }
    /**
     * String.format打印最简便
     */
    publicvoid m3() {
        System.out.println(String.format("%.2f", f));
    }
    publicvoid m4() {
        NumberFormat nf = NumberFormat.getNumberInstance();
        nf.setMaximumFractionDigits(2);
        System.out.println(nf.format(f));
    }
    public staticvoid main(String[] args) {
        format f = new format();
        f.m1();
        f.m2();
        f.m3();
        f.m4();
    }
}

结果：

111231.56

111231.56

111231.56

111,231.56