public class DecimalUtils {

    //保留2位,不足补0

    private static final DecimalFormat df_fill_zero = new DecimalFormat("00.00");

    //保留2位,不足保留原位数

    private static final DecimalFormat df_fill_null = new DecimalFormat("##.##");

    public static void main (String args[]) {

        System.out.println(df_fill_zero.format(1.2)); //01.20  不足2位补0

        System.out.println(df_fill_null.format(1.2)); //1.2   不足2位保留原数位

        System.out.println(df_fill_zero.format(1.224)); //01.22 超出2位截断(舍入模式后面再说)

        System.out.println(df_fill_null.format(1.224)); //1.22 超出2位截断(舍入模式后面再说)

        System.out.println(df_fill_zero.format(123.22)); //123.22

        System.out.println(df_fill_null.format(123.22)); //123.22

    }

}

01.20

1.2

01.22

1.22

123.22

123.22

public class FormatDefault {

  //保留3位,不足保留原位数

    private static final DecimalFormat df_t = new DecimalFormat("#.###");

    public static void main (String args[]) {

        //默认舍入模式（RoundingMode.HALF_EVEN）

        System.out.println(df_t.format(1234.2224)); //1234.222

        System.out.println(df_t.format(1234.2226)); //1234.223

        System.out.println(df_t.format(1234.2225)); //1234.223  最后一位偶数，舍入

        System.out.println(df_t.format(1234.2235)); //1234.223  最后一位奇数，舍去

    }

}

public class FormatHalfUp {

    /***

     * 最多保存3位小数,如果number少于3位则保留原小数位数,如果多于3位则四舍五入保留3位小数

     */

    public static String formatHalfUp(double number) {

        DecimalFormat df = new DecimalFormat("#.###");

        df.setRoundingMode(RoundingMode.HALF_UP);

        return df.format(BigDecimal.valueOf(number)); //防止精度丢失，数字类型用BigDecimal

    }

    public static void main (String args[]) {

        //四舍五入舍入模式（RoundingMode.HALF_UP）

        System.out.println(formatHalfUp(1234.2224)); //1234.222

        System.out.println(formatHalfUp(1234.2226)); //1234.223

        System.out.println(formatHalfUp(1234.2225)); //1234.223

        System.out.println(formatHalfUp(1234.2235)); //1234.224

    }

}