---
title: BigDecimal
category: Java
tag:
- Java
---
## BigDecimal
`BigDecimal` `BigDecimal`
```java
float a = 2.0f - 1.9f;
float b = 1.8f - 1.7f;
System.out.println(a);// 0.100000024
System.out.println(b);// 0.099999905
System.out.println(a == b);// false
```
** `float` `double` **
0.2
```java
// 0.2 2
//
0.2 * 2 = 0.4 -> 0
0.4 * 2 = 0.8 -> 0
0.8 * 2 = 1.6 -> 1
0.6 * 2 = 1.2 -> 1
0.2 * 2 = 0.4 -> 0
...
```
[](http://kaito-kidd.com/2018/08/08/computer-system-float-point/)
## BigDecimal
Java **== equals **
```java
float a = 1.0f - 0.9f;
float b = 0.9f - 0.8f;
System.out.println(a);// 0.100000024
System.out.println(b);// 0.099999964
System.out.println(a == b);// false
```
`BigDecimal`
```java
BigDecimal a = new BigDecimal("1.0");
BigDecimal b = new BigDecimal("0.9");
BigDecimal c = new BigDecimal("0.8");
BigDecimal x = a.subtract(b);
BigDecimal y = b.subtract(c);
System.out.println(x); /* 0.1 */
System.out.println(y); /* 0.1 */
System.out.println(Objects.equals(x, y)); /* true */
```
## BigDecimal
###
`add` `BigDecimal` `subtract` `BigDecimal` `multiply` `BigDecimal` `divide` `BigDecimal`
```java
BigDecimal a = new BigDecimal("1.0");
BigDecimal b = new BigDecimal("0.9");
System.out.println(a.add(b));// 1.9
System.out.println(a.subtract(b));// 0.1
System.out.println(a.multiply(b));// 0.90
System.out.println(a.divide(b));// ArithmeticException
System.out.println(a.divide(b, 2, RoundingMode.HALF_UP));// 1.11
```
`divide` 3 `RoundingMode` `UNNECESSARY` `ArithmeticException` `scale` `roundingMode`
```java
public BigDecimal divide(BigDecimal divisor, int scale, RoundingMode roundingMode) {
return divide(divisor, scale, roundingMode.oldMode);
}
```
:
```java
public enum RoundingMode {
// 2.5 -> 3 , 1.6 -> 2
// -1.6 -> -2 , -2.5 -> -3
UP(BigDecimal.ROUND_UP),
// 2.5 -> 2 , 1.6 -> 1
// -1.6 -> -1 , -2.5 -> -2
DOWN(BigDecimal.ROUND_DOWN),
// 2.5 -> 3 , 1.6 -> 2
// -1.6 -> -1 , -2.5 -> -2
CEILING(BigDecimal.ROUND_CEILING),
// 2.5 -> 2 , 1.6 -> 1
// -1.6 -> -2 , -2.5 -> -3
FLOOR(BigDecimal.ROUND_FLOOR),
// 2.5 -> 3 , 1.6 -> 2
// -1.6 -> -2 , -2.5 -> -3
HALF_UP(BigDecimal.ROUND_HALF_UP),
//......
}
```
###
`a.compareTo(b)` : -1 `a` `b`0 `a` `b` 1 `a` `b`
```java
BigDecimal a = new BigDecimal("1.0");
BigDecimal b = new BigDecimal("0.9");
System.out.println(a.compareTo(b));// 1
```
###
`setScale`IDEA
```java
BigDecimal m = new BigDecimal("1.255433");
BigDecimal n = m.setScale(3,RoundingMode.HALF_DOWN);
System.out.println(n);// 1.255
```
## BigDecimal
`BigDecimal` `BigDecimal(String val)` `BigDecimal.valueOf(double val)`
Java
## BigDecimal
`BigDecimal` `BigDecimal`
```java
import java.math.BigDecimal;
import java.math.RoundingMode;
/**
* BigDecimal
*/
public class BigDecimalUtil {
/**
*
*/
private static final int DEF_DIV_SCALE = 10;
private BigDecimalUtil() {
}
/**
*
*
* @param v1
* @param v2
* @return
*/
public static double add(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.add(b2).doubleValue();
}
/**
*
*
* @param v1
* @param v2
* @return
*/
public static double subtract(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.subtract(b2).doubleValue();
}
/**
*
*
* @param v1
* @param v2
* @return
*/
public static double multiply(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.multiply(b2).doubleValue();
}
/**
*
* 10
*
* @param v1
* @param v2
* @return
*/
public static double divide(double v1, double v2) {
return divide(v1, v2, DEF_DIV_SCALE);
}
/**
* scale
*
*
* @param v1
* @param v2
* @param scale
* @return
*/
public static double divide(double v1, double v2, int scale) {
if (scale < 0) {
throw new IllegalArgumentException(
"The scale must be a positive integer or zero");
}
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.divide(b2, scale, RoundingMode.HALF_UP).doubleValue();
}
/**
*
*
* @param v
* @param scale
* @return
*/
public static double round(double v, int scale) {
if (scale < 0) {
throw new IllegalArgumentException(
"The scale must be a positive integer or zero");
}
BigDecimal b = BigDecimal.valueOf(v);
BigDecimal one = new BigDecimal("1");
return b.divide(one, scale, RoundingMode.HALF_UP).doubleValue();
}
/**
* (Float)
*
* @param v
* @return
*/
public static float convertToFloat(double v) {
BigDecimal b = new BigDecimal(v);
return b.floatValue();
}
/**
* (Int)
*
* @param v
* @return
*/
public static int convertsToInt(double v) {
BigDecimal b = new BigDecimal(v);
return b.intValue();
}
/**
* (Long)
*
* @param v
* @return
*/
public static long convertsToLong(double v) {
BigDecimal b = new BigDecimal(v);
return b.longValue();
}
/**
*
*
* @param v1
* @param v2
* @return
*/
public static double returnMax(double v1, double v2) {
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.max(b2).doubleValue();
}
/**
*
*
* @param v1
* @param v2
* @return
*/
public static double returnMin(double v1, double v2) {
BigDecimal b1 = new BigDecimal(v1);
BigDecimal b2 = new BigDecimal(v2);
return b1.min(b2).doubleValue();
}
/**
*
*
* @param v1
* @param v2
* @return 01-1
*/
public static int compareTo(double v1, double v2) {
BigDecimal b1 = BigDecimal.valueOf(v1);
BigDecimal b2 = BigDecimal.valueOf(v2);
return b1.compareTo(b2);
}
}
```
##
`BigDecimal` `BigInteger` `long`
`BigDecimal` `BigInteger`, `BigDecimal`