double或Double取整或保留n位小数(后续如果有需要再整理其他小数类型)

傷城~ 2023-10-09 15:09 3阅读 0赞

## 1. double或Double取整或保留n位小数 ##

**参考链接：**

*  [Java中double保留两位小数的四种方法 - 古家杰 - 博客园 (cnblogs.com)][Java_double_ - _ - _ _cnblogs.com]
 *  [java double类型保留两位小数4种方法\_huaism的博客-CSDN博客][java double_4_huaism_-CSDN]

### 1.1 double取整 ###

#### 1.1.1 Math.floor()向上取整 ####

/**
      * Math.floor()向上取整：通过该函数计算后的返回值是舍去小数点后的数值
      */
     double floor = Math.floor(3.0);
     System.out.println("floor = " + floor);// floor = 3.0
     double floor1 = Math.floor(3.3);
     System.out.println("floor1 = " + floor1);// floor1 = 3.0
     double floor2 = Math.floor(3.7);
     System.out.println("floor2 = " + floor2);// floor2 = 3.0

#### 1.1.2 Math.ceil()向下取整 ####

/**
      *  Math.ceil()向下取整：ceil函数只要小数点非0，将返回整数部分+1
      */
     double ceil = Math.ceil(4.0);
     System.out.println("ceil = " + ceil);// ceil = 4.0
     double ceil1 = Math.ceil(4.3);
     System.out.println("ceil1 = " + ceil1);// ceil1 = 5.0
     double ceil2 = Math.ceil(4.8);
     System.out.println("ceil2 = " + ceil2);// ceil1 = 5.0

### 1.2 double保留1位小数 ###

double decimal = 3.1415926;
     
     // 1. 使用BigDecimal的setScale方法
     BigDecimal oneDecimal = new BigDecimal(decimal);
     double v1 = oneDecimal.setScale(1, BigDecimal.ROUND_HALF_UP).doubleValue();
     System.out.println("v1 = " + v1);// v1 = 3.1
     
     // 2. 使用DecimalFormat
     DecimalFormat format1 = new DecimalFormat("#.0");
     String format11 = format1.format(decimal);
     double v11 = Double.parseDouble(format11);
     System.out.println("v11 = " + v11);// v11 = 3.1
     
     // 3. 使用Sting自带的format方法
     String format111 = String.format("%.1f", decimal);
     double v111 = Double.parseDouble(format111);
     System.out.println("v111 = " + v111);// v111 = 3.1
     
     // 4. 使用NumberFormat设置最大小数位数
     NumberFormat instance1111= NumberFormat.getInstance();
     instance1111.setMaximumFractionDigits(1);
     String format1111 = instance1111.format(decimal);
     double v1111 = Double.parseDouble(format1111);
     System.out.println("v1111 = " + v1111);// v11111 = 3.1
     // 或
     NumberFormat numberInstance11111 = NumberFormat.getNumberInstance();
     numberInstance11111.setMaximumFractionDigits(1);
     String format11111 = numberInstance11111.format(decimal);
     double v11111 = Double.parseDouble(format11111);
     System.out.println("v11111 = " + v11111);// v22222 = 3.14

### 1.3 double保留2位小数 ###

double decimal = 3.1415926;
     
     // 1. 使用BigDecimal的setScale方法
     BigDecimal twoDecimal = new BigDecimal(decimal);
     double v2 = twoDecimal.setScale(2, BigDecimal.ROUND_HALF_UP).doubleValue();
     System.out.println("v2 = " + v2);// v2 = 3.14
     
     // 2. 使用DecimalFormat
     DecimalFormat format2 = new DecimalFormat("#.00");
     String format22 = format2.format(decimal);
     double v22 = Double.parseDouble(format22);
     System.out.println("v22 = " + v22);// v22 = 3.14
     
     // 3. 使用Sting自带的format方法
     String format222 = String.format("%.2f", decimal);
     double v222 = Double.parseDouble(format222);
     System.out.println("v222 = " + v222);// v222 = 3.14
     
     // 4. 使用NumberFormat设置最大小数位数
     NumberFormat instance2222 = NumberFormat.getInstance();
     instance2222.setMaximumFractionDigits(2);
     String format2222 = instance2222.format(decimal);
     double v2222 = Double.parseDouble(format2222);
     System.out.println("v2222 = " + v2222);// v2222 = 3.14
     // 或
     NumberFormat numberInstance22222 = NumberFormat.getNumberInstance();
     numberInstance22222.setMaximumFractionDigits(2);
     String format22222 = numberInstance22222.format(decimal);
     double v22222 = Double.parseDouble(format22222);
     System.out.println("v22222 = " + v22222);// v22222 = 3.14

[Java_double_ - _ - _ _cnblogs.com]: https://www.cnblogs.com/gujiajie/p/16338812.html
[java double_4_huaism_-CSDN]: https://blog.csdn.net/huaishuming/article/details/17752365