1. double或Double取整或保留n位小数
1.1 double取整
1.1.1 ()向下取整
功能说明：
-
floor这个单词用作名词可以表示为地板，第一印象可以理解为向下；
-
floor函数的意思就是向下取整，如果原先的数值为x，那么它返回不大于x的最大整数，即返回的整数≤x。
测试代码：
package test_2024;
import ;
import ;
import ;
/**
* @ClassName Test2024010701
* @Description TODO
* @Author Jiangnan Cui
* @Date 2024/1/7 17:19
* @Version 1.0
*/
public class Test2024010701 {
public static void main(String[] args) {
// 1.正数
double floor1 = (3.0);
("floor1 = " + floor1);
// floor1 = 3.0
double floor2 = (3.1);
("floor2 = " + floor2);
// floor2 = 3.0
double floor3 = (3.4);
("floor3 = " + floor3);
// floor3 = 3.0
double floor4 = (3.5);
("floor4 = " + floor4);
// floor4 = 3.0
double floor5 = (3.7);
("floor5 = " + floor5);
// floor5 = 3.0
// 2.负数
double floor11 = (-3.0);
("floor11 = " + floor11);
// floor11 = -3.0
double floor21 = (-3.1);
("floor21 = " + floor21);
// floor21 = -4.0
double floor31 = (-3.4);
("floor31 = " + floor31);
// floor31 = -4.0
double floor41 = (-3.5);
("floor41 = " + floor41);
// floor41 = -4.0
double floor51 = (-3.7);
("floor51 = " + floor51);
// floor51 = -4.0
}
}1.1.2 ()向上取整
功能说明：
-
ceil这个单词用作名词可以表示为天花板，第一印象可以理解为向上；
-
ceil函数的意思就是向上取整，如果原先的数值为x，那么它返回不小于x的最大整数，即返回的整数≥x。
测试代码
package test_2024;
/**
* @ClassName Test2024010702
* @Description TODO
* @Author Jiangnan Cui
* @Date 2024/1/7 17:22
* @Version 1.0
*/
public class Test2024010702 {
public static void main(String[] args) {
// 1.正数
double ceil1 = (3.0);
("ceil1 = " + ceil1);
// ceil1 = 3.0
double ceil2 = (3.1);
("ceil2 = " + ceil2);
// ceil2 = 4.0
double ceil3 = (3.4);
("ceil3 = " + ceil3);
// ceil3 = 4.0
double ceil4 = (3.5);
("ceil4 = " + ceil4);
// ceil4 = 4.0
double ceil5 = (3.7);
("ceil5 = " + ceil5);
// ceil5 = 4.0
// 2.负数
double ceil11 = (-3.0);
("ceil11 = " + ceil11);
// ceil11 = -3.0
double ceil21 = (-3.1);
("ceil21 = " + ceil21);
// ceil21 = -3.0
double ceil31 = (-3.4);
("ceil31 = " + ceil31);
// ceil31 = -3.0
double ceil41 = (-3.5);
("ceil41 = " + ceil41);
// ceil41 = -3.0
double ceil51 = (-3.7);
("ceil51 = " + ceil51);
// ceil51 = -3.0
}
}1.2 double保留x位小数
1.2.1 保留1位
测试代码：
package test_2024;
import ;
import ;
import ;
/**
* @ClassName Test2024010703
* @Description TODO
* @Author Jiangnan Cui
* @Date 2024/1/7 17:24
* @Version 1.0
*/
public class Test2024010703 {
public static void main(String[] args) {
double decimal = 3.1415926;
// 1. 使用BigDecimal的setScale方法
BigDecimal bigDecimal = new BigDecimal(decimal);
double bigDecimalDouble = (1, BigDecimal.ROUND_HALF_UP).doubleValue();
("bigDecimalDouble = " + bigDecimalDouble);
// bigDecimalDouble = 3.1
// 2. 使用DecimalFormat
DecimalFormat decimalFormat = new DecimalFormat("#.0");
String formatDecimalString = (decimal);
double doubleDecimal = (formatDecimalString);
("doubleDecimal = " + doubleDecimal);
// doubleDecimal = 3.1
// 3. 使用String自带的format方法
String stringFormat = ("%.1f", decimal);
// String stringFormat = ("%.1f", decimal);
// 注意此处不能用，因为上面输出结果是%.1f，会产生NumberFormatException
double stringFormatDouble = (stringFormat);
("stringFormatDouble = " + stringFormatDouble);
// stringFormatDouble = 3.1
// 4. 使用NumberFormat设置最大小数位数
NumberFormat numberFormat = ();
(1);
String numberFormatString = (decimal);
double numberFormatDouble = (numberFormatString);
("numberFormatDouble = " + numberFormatDouble);
// numberFormatDouble = 3.1
// 或
NumberFormat numberFormat11 = ();
(1);
String numberFormat11String = (decimal);
double numberFormat11Double = (numberFormat11String);
("numberFormat11Double = " + numberFormat11Double);
// numberFormat11Double = 3.1
}
}1.2.2 保留2位
测试代码：
package test_2024;
import ;
import ;
import ;
/**
* @ClassName Test2024070704
* @Description TODO
* @Author Jiangnan Cui
* @Date 2024/1/7 17:26
* @Version 1.0
*/
public class Test2024070704 {
public static void main(String[] args) {
double decimal = 3.1415926;
// 1. 使用BigDecimal的setScale方法
BigDecimal bigDecimal2 = new BigDecimal(decimal);
double bigDecimal2Double = (2, BigDecimal.ROUND_HALF_UP).doubleValue();
("bigDecimal2Double = " + bigDecimal2Double);
// bigDecimal2Double = 3.14
// 2. 使用DecimalFormat
DecimalFormat decimalFormat2 = new DecimalFormat("#.00");
String decimalFormat2String = (decimal);
double decimalFormat2Double = (decimalFormat2String);
("decimalFormat2Double = " + decimalFormat2Double);
// decimalFormat2Double = 3.14
// 3. 使用Sting自带的format方法
String stringFormat2 = ("%.2f", decimal);
// String stringFormat2 = ("%.2f", decimal);
// 注意此处不能用，因为上面输出结果是%.2f，会产生NumberFormatException
double stringFormat2Double = (stringFormat2);
("stringFormat2Double = " + stringFormat2Double);
// stringFormat2Double = 3.14
// 4. 使用NumberFormat设置最大小数位数
NumberFormat numberFormat2 = ();
(2);
String numberFormat2String = (decimal);
double numberFormat2Double = (numberFormat2String);
("numberFormat2Double = " + numberFormat2Double);
// numberFormat2Double = 3.14
// 或
NumberFormat numberFormat22 = ();
(2);
String numberFormat22String = (decimal);
double numberFormat22Double = (numberFormat22String);
("numberFormat22Double = " + numberFormat22Double);
// numberFormat22Double = 3.14
}
}