Java Data Type - 如何使用half down, floor, ceiling对数字进行处理

import java.math.RoundingMode;
import java.text.NumberFormat;

public class NumberFormatRounding {
  public static void main(String[] args) {
    NumberFormat nf = NumberFormat.getNumberInstance();
    nf.setMaximumFractionDigits(2);
    nf.setRoundingMode (RoundingMode.HALF_DOWN);
    System.out.println("Default rounding mode: " + nf.getRoundingMode());
    System.out.println("123.454 rounds to " + nf.format(123.454));
    System.out.println("123.455 rounds to " + nf.format(123.455));
    System.out.println("123.456 rounds to " + nf.format(123.456));
    System.out.println();

    nf.setRoundingMode (RoundingMode.FLOOR);
    System.out.println("Default rounding mode: " + nf.getRoundingMode());
    System.out.println("123.454 rounds to " + nf.format(123.454));
    System.out.println("123.455 rounds to " + nf.format(123.455));
    System.out.println("123.456 rounds to " + nf.format(123.456));
    System.out.println();

    nf.setMaximumFractionDigits(2);
    nf.setRoundingMode (RoundingMode.CEILING);
    System.out.println("Default rounding mode: " + nf.getRoundingMode());
    System.out.println("123.454 rounds to " + nf.format(123.454));
    System.out.println("123.455 rounds to " + nf.format(123.455));
    System.out.println("123.456 rounds to " + nf.format(123.456));
    System.out.println();

  }
}